various crates: MSRV TODO standardization and cleanup of an old TODO

tor-netdir:

• Removed a #[allow(clippy::map_identity)], as https://github.com/rust-lang/rust-clippy/issues/11764 was fixed upstream.

arti-relay:

tor-basic-utils:

tor-consdiff:

tor-hsservice:

tor-memquota:

tor-rpc-connect:

• TODOs related to MSRV changes have been changed to start with the form TODO MSRV X where X is either:
  • TBD for unstable features we want once they are stabilized and our MSRV reaches the stabilized version.
  • Y.ZZ for stable features that were stabilized in Rust version Y.ZZ.

The intention with this is to make it easier to find and deal with these TODOs when the MSRV reaches the designated version.

/cc @nickm You made this TODO about str::split_inclusive 4 years ago, do you still think switching to using it is preferable? Looking at the tests, it seems we expect each line to end with \n, is there any reason we'd need to be concerned about \r or \r\n?