Allow "clippy::single_char_pattern" in tests.

This lint exists for perf reasons, and this is rarely relevant in
tests.

Using double quoted str is generally cognitively less burdensome.

crates/arti-client/examples/advanced_isolation.rs

@@ -4,6 +4,7 @@
 #![allow(clippy::dbg_macro)]
 #![allow(clippy::print_stderr)]
 #![allow(clippy::print_stdout)]
+#![allow(clippy::single_char_pattern)]
 #![allow(clippy::unwrap_used)]
 //! <!-- @@ end test lint list maintained by maint/add_warning @@ -->
 

crates/arti-client/examples/hook-tcp.rs

@@ -4,6 +4,7 @@
 #![allow(clippy::dbg_macro)]
 #![allow(clippy::print_stderr)]
 #![allow(clippy::print_stdout)]
+#![allow(clippy::single_char_pattern)]
 #![allow(clippy::unwrap_used)]
 //! <!-- @@ end test lint list maintained by maint/add_warning @@ -->
 

crates/arti-client/examples/lazy-init.rs

@@ -4,6 +4,7 @@
 #![allow(clippy::dbg_macro)]
 #![allow(clippy::print_stderr)]
 #![allow(clippy::print_stdout)]
+#![allow(clippy::single_char_pattern)]
 #![allow(clippy::unwrap_used)]
 //! <!-- @@ end test lint list maintained by maint/add_warning @@ -->
 

crates/arti-client/examples/readme.rs

@@ -4,6 +4,7 @@
 #![allow(clippy::dbg_macro)]
 #![allow(clippy::print_stderr)]
 #![allow(clippy::print_stdout)]
+#![allow(clippy::single_char_pattern)]
 #![allow(clippy::unwrap_used)]
 //! <!-- @@ end test lint list maintained by maint/add_warning @@ -->
 

crates/arti-hyper/examples/hyper.rs

@@ -4,6 +4,7 @@
 #![allow(clippy::dbg_macro)]
 #![allow(clippy::print_stderr)]
 #![allow(clippy::print_stdout)]
+#![allow(clippy::single_char_pattern)]
 #![allow(clippy::unwrap_used)]
 //! <!-- @@ end test lint list maintained by maint/add_warning @@ -->
 

crates/arti/src/cfg.rs

@@ -234,6 +234,7 @@ mod test {
     #![allow(clippy::dbg_macro)]
     #![allow(clippy::print_stderr)]
     #![allow(clippy::print_stdout)]
+    #![allow(clippy::single_char_pattern)]
     #![allow(clippy::unwrap_used)]
     //! <!-- @@ end test lint list maintained by maint/add_warning @@ -->
 

crates/tor-basic-utils/src/futures.rs

@@ -516,6 +516,7 @@ mod test {
     #![allow(clippy::dbg_macro)]
     #![allow(clippy::print_stderr)]
     #![allow(clippy::print_stdout)]
+    #![allow(clippy::single_char_pattern)]
     #![allow(clippy::unwrap_used)]
     //! <!-- @@ end test lint list maintained by maint/add_warning @@ -->
 

crates/tor-basic-utils/src/n_key_set.rs

@@ -461,6 +461,7 @@ mod test {
     #![allow(clippy::dbg_macro)]
     #![allow(clippy::print_stderr)]
     #![allow(clippy::print_stdout)]
+    #![allow(clippy::single_char_pattern)]
     #![allow(clippy::unwrap_used)]
     //! <!-- @@ end test lint list maintained by maint/add_warning @@ -->
 

crates/tor-chanmgr/src/config.rs

@@ -40,6 +40,7 @@ mod test {
     #![allow(clippy::dbg_macro)]
     #![allow(clippy::print_stderr)]
     #![allow(clippy::print_stdout)]
+    #![allow(clippy::single_char_pattern)]
     #![allow(clippy::unwrap_used)]
     //! <!-- @@ end test lint list maintained by maint/add_warning @@ -->
     use super::*;

crates/tor-chanmgr/src/mgr/map.rs

@@ -579,6 +579,7 @@ mod test {
     #![allow(clippy::dbg_macro)]
     #![allow(clippy::print_stderr)]
     #![allow(clippy::print_stdout)]
+    #![allow(clippy::single_char_pattern)]
     #![allow(clippy::unwrap_used)]
     //! <!-- @@ end test lint list maintained by maint/add_warning @@ -->
 

crates/tor-chanmgr/src/mgr/map/padding_test.rs

@@ -6,6 +6,7 @@
 #![allow(clippy::dbg_macro)]
 #![allow(clippy::print_stderr)]
 #![allow(clippy::print_stdout)]
+#![allow(clippy::single_char_pattern)]
 #![allow(clippy::unwrap_used)]
 //! <!-- @@ end test lint list maintained by maint/add_warning @@ -->
 

crates/tor-circmgr/src/path/dirpath.rs

@@ -91,6 +91,7 @@ mod test {
     #![allow(clippy::dbg_macro)]
     #![allow(clippy::print_stderr)]
     #![allow(clippy::print_stdout)]
+    #![allow(clippy::single_char_pattern)]
     #![allow(clippy::unwrap_used)]
     //! <!-- @@ end test lint list maintained by maint/add_warning @@ -->
 

crates/tor-config/src/misc.rs

@@ -313,6 +313,7 @@ mod test {
     #![allow(clippy::dbg_macro)]
     #![allow(clippy::print_stderr)]
     #![allow(clippy::print_stdout)]
+    #![allow(clippy::single_char_pattern)]
     #![allow(clippy::unwrap_used)]
     //! <!-- @@ end test lint list maintained by maint/add_warning @@ -->
     use super::*;

crates/tor-config/src/path.rs

@@ -338,6 +338,7 @@ mod test_serde {
     #![allow(clippy::dbg_macro)]
     #![allow(clippy::print_stderr)]
     #![allow(clippy::print_stdout)]
+    #![allow(clippy::single_char_pattern)]
     #![allow(clippy::unwrap_used)]
     //! <!-- @@ end test lint list maintained by maint/add_warning @@ -->
 

crates/tor-config/src/sources.rs

@@ -406,6 +406,7 @@ mod test {
     #![allow(clippy::dbg_macro)]
     #![allow(clippy::print_stderr)]
     #![allow(clippy::print_stdout)]
+    #![allow(clippy::single_char_pattern)]
     #![allow(clippy::unwrap_used)]
     //! <!-- @@ end test lint list maintained by maint/add_warning @@ -->
 

crates/tor-error/src/internal.rs

@@ -253,6 +253,7 @@ mod test {
     #![allow(clippy::dbg_macro)]
     #![allow(clippy::print_stderr)]
     #![allow(clippy::print_stdout)]
+    #![allow(clippy::single_char_pattern)]
     #![allow(clippy::unwrap_used)]
     //! <!-- @@ end test lint list maintained by maint/add_warning @@ -->
     use super::*;

crates/tor-guardmgr/src/bridge/config.rs

@@ -380,6 +380,7 @@ mod test {
     #![allow(clippy::dbg_macro)]
     #![allow(clippy::print_stderr)]
     #![allow(clippy::print_stdout)]
+    #![allow(clippy::single_char_pattern)]
     #![allow(clippy::unwrap_used)]
     //! <!-- @@ end test lint list maintained by maint/add_warning @@ -->
     use super::*;

crates/tor-guardmgr/src/fallback/set.rs

@@ -241,6 +241,7 @@ mod test {
     #![allow(clippy::dbg_macro)]
     #![allow(clippy::print_stderr)]
     #![allow(clippy::print_stdout)]
+    #![allow(clippy::single_char_pattern)]
     #![allow(clippy::unwrap_used)]
     //! <!-- @@ end test lint list maintained by maint/add_warning @@ -->
 

crates/tor-proto/src/channel/padding.rs

@@ -409,6 +409,7 @@ mod test {
     #![allow(clippy::dbg_macro)]
     #![allow(clippy::print_stderr)]
     #![allow(clippy::print_stdout)]
+    #![allow(clippy::single_char_pattern)]
     #![allow(clippy::unwrap_used)]
     //! <!-- @@ end test lint list maintained by maint/add_warning @@ -->
 

crates/tor-socksproto/src/handshake.rs

@@ -90,6 +90,7 @@ mod test_roundtrip {
     #![allow(clippy::dbg_macro)]
     #![allow(clippy::print_stderr)]
     #![allow(clippy::print_stdout)]
+    #![allow(clippy::single_char_pattern)]
     #![allow(clippy::unwrap_used)]
     //! <!-- @@ end test lint list