feat: LuaCov support

[luau-project]

Closes # (issue)

N/A

⚡ Summary

Adds support for the default format generated by LuaCov (https://github.com/lunarmodules/luacov), popularly known as the "standard" coverage tool for Lua (https://lua.org) code.

☑️ Checklist

• [ x ] Added a parser to consume LuaCov reports
• [ x ] Add specs
• [ x ] Updated subsequent docs on README

Details

I was motivated by the official (guide) to add LuaCov support.

Important

I didn't use any LLM code, and I have a total of 3 days of experience with the Crystal lang.

Points that I judge relevant to this PR:

1. I wrote a custom parser for the LuaCov report format. This led to a high cyclomatic complexity running the linter. For this reason, I decided to exclude LuaCov from the cyclomatic check, but the code is well commented;
2. Locally, I certified myself that I was able to:
   • build the project (make)
   • run the test suite (make test)
   • run the linter (make lint) and
   • also the coverage (bin/crkcov --kcov-args --exclude-pattern=/usr/include,/usr/lib,lib/,spec/ --coverage-dir <project dir>/coverage) asserting that luacov_parser.cr achieves a high coverage (over 90%);
3. I also ran the built bin/coveralls on a personal project in dry-run mode, and everything worked nicely;
4. I also ran CI (ci.yml) on my fork before opening this PR.

[codacy-production]

Up to standards ✅

🟢 Issues 0 issues

Results:
0 new issues

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