Support more regex engines for testing

[Aloso]

Is your feature request related to a problem? Please describe.

Currently, tests can only be executed with PCRE2. They should be executable with a regex engine for every flavor. Also, the --test <ENGINE> CLI interface is confusing.

Describe the solution you'd like

Extend the supported engines to include at least the following:

• pcre2
• rust
• onig
• python
• node
• deno
• java

Getting C# to work cross-platform is more tricky, which is why it isn't included in this list for now.

Strategies

• Rust, Oniguruma: Regex engine is statically linked in the executable
• Python: python3 -c ...; fallback to python executable if unavailable
• Node: node -e ...
• Deno: deno eval ...
• Java: java with a temporary class file

Batch checking

A command that tests all pomsky expressions in a directory would be immensely helpful, e.g. for pre-commit hooks and CI. It should

• walk the provided directory recursively, respecting .gitignore and .pomskyignore files
• follow symlinks ??
• compile and test all files with a .pomsky extension
• if not using a statically linked regex library, re-use the process that does the testing for all files (similarly to regex-test)
• provide a summary (number of succeeded/failed tests) and errors

[fundef1]

any chance for RE2 support? (go and DuckDB for instance).
I'm using pomsky to generate regexes (w/o the features RE2 lacks) so testing with PCRE is equivalent but having this checked off during tests would be nice.

[Aloso]

Rust is now supported.