Rust: add tests for protover edge cases
There are more tests for legacy/trac#27164 and legacy/trac#27177 in branch prototest1 on ​https://gitgud.io/onionk/tor.git Since we backported the fixes, I suggest we backport the tests. Original comment: https://trac.torproject.org/projects/tor/ticket/27164#comment:7
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