Now that we require Rust 1.56, we can upgrade to AES 0.8.  This
forces us to have some slight API changes.

We require cipher 0.4.1, not cipher 0.4.0, since 0.4.0 has
compatibility issues with Rust 1.56.

Now that our MSRV is at 1.56, we can use the latest rlimit.

It has to be 0.8.3 (not "0.8"), since 0.8.2 has compatibility issues
with 1.56.

Increase our MSRV to 1.56.

See merge request tpo/core/arti!472

# Conflicts:
#   crates/tor-config/Cargo.toml
#   crates/tor-dirmgr/src/state.rs
#   doc/semver_status.md

Introduce macro for ThingListBuilder, and use for AuthorityListBuilder

See merge request tpo/core/arti!471

retry-error: Provide AbsRetryTime::from_sub and use it

See merge request tpo/core/arti!470

As requested in
  tpo/core/arti!470 (comment 2798015)

As per
  tpo/core/arti!470 (comment 2797945)

Because the macro output is private, if we miss one out of the tests,
it doesn't fail due to dead code :-).

Really, we probably don't want any of these not to be pub, but it
triggers "unreachable pub" in my test cases, and making it not pub by
mistake seems not very serious, and likely to be noticed.

Making the struct private in the test cases has the useful effect of
checking that all the methods are tested.

I don't think we need to bother with things in the prelude,
but doing it for serde and ConfigBuildError seems nice.

Noticed while writing a test case.

And add an imprecation in define_list_config_builder's doc comment do
do so in future for other invocations of the macro.

Add add the missing full stops.

As per
  tpo/core/arti!471 (comment 2798027)

Requested in
  tpo/core/arti!471 (comment 2798022)

These were omitted in the earlier commits.

As per
  tpo/core/arti!471 (comment 2798026)

As per
  !471 (comment 2798024)

Remove all `use` statements for `TryFrom` and `TryInto`.  These are
now redundant in Rust 2021.

This is an automated change made with a perl one-liner and verified
with grep -L and grep -l.

Some warnings are introduced with this change; they will be removed
in subsequent commits.

See arti#208 for older discussion on this issue.

This change was made automatically with a perl one-liner, and
confirmed with `grep -L`.

The `rust-version` field itself was introduced in 1.56.0.

There are no semantic changes here; only formatting.  This is in
preparation for other changes (wrt MSRV and edition)

Our support policy says that we can update to any Rust released at
least 6 months ago; 1.56 came out on 21 October 2021.

This doesn't yet change any code: it just increases the version
we say we need in our README, and the version we test against in
CI.

Our main justification for this change is to be able to upgrade to
newer versions of our dependencies, including `async_executors` >=
0.5, `aes` >= 0.8, and `cipher` >= 0.4.

As per
  tpo/core/arti!471 (comment 2798020)

This means that `NetworkConfig::initial_predicted_ports` is now like
the other list-like things, returning `&mut list_builder` with the same
`set()` and `append()` methods.

This will be useful especially for simple lists where the entry
doesn't need a separate builder type.

NetworkConfigBuilder needs to not contain any validated structs, so
that its serde does not expose the validated details.

AuthorityListBuilder is what ought to go here - and it contains
Vec<AuthorityBuilder>, not Vec<Authority>.  As a consequence, many
places now deal with AuthorityBuilder, rather than Authority.

This replaces two almost-identical sets of structs and impls.  More
are on the way, as per
  tpo/core/arti#447

Since "logfiles: Introduce LogfileListConfigBuilder", this code is in
LogfileListConfigBuilder::build(), which is called by derive_builder's
generated LoggingConfig::build(), and which will add a file context
itself due to the `sub_builder` feature.

So this is otiose.  And, we are about to replace this whole thing with
macro_rules-generated code (which won't do this).

Better handling of integer overflows

See merge request tpo/core/arti!466

This same calculation was in the code three times.

Authority: make v3ident public under experimental-api

See merge request tpo/core/arti!463

Fix typos bothering rust-nightly pipeline

See merge request tpo/core/arti!464

tor-basic-utils: Add RetryDelay::reset test

See merge request tpo/core/arti!467