* ADD new protover::protoset module.
* ADD new protover::protoset::ProtoSet class for holding protover versions.
* REMOVE protover::Versions type implementation and its method
`from_version_string()`, and instead implement this behaviour in a more
rust-like manner as `impl FromStr for ProtoSet`.
* MOVE the `find_range()` utility function from protover::protover to
protover::protoset since it's only used internally in the
implementation of ProtoSet.
* REMOVE the `contract_protocol_list()` function from protover::protover and
instead refactor it (reusing nearly the entire thing, with minor superficial,
i.e. non-behavioural, changes) into a more rusty
`impl ToString for ProtoSet`.
* REMOVE the `expand_version_range()` function from protover::protover and
instead refactor it into a more rusty implementation of
`impl Into<Vec<Version>> for ProtoSet` using the new error types in
protover::errors.
* FIXES part of #24031: https://bugs.torproject.org/24031.
This will allow us to do actual error handling intra-crate in a more
rusty manner, e.g. propogating errors in match statements, conversion
between error types, logging messages, etc.
* FIXES part of #24031: https://bugs.torproject.org/24031.
* FIXES#25127: https://bugs.torproject.org/25127
* ADDS a new module to the Rust tor_util crate for small utilities
for working with static strings between languages.
* CHANGES the return type of protover_compute_for_old_tor to point to
immutable data.
* CHANGES the code from the previous commit to use the new static
string utilities.
