feat: add Ruby tooling support (rspec, rake, bundler)

Context

rtk has solid coverage for JS/TS, Python, Go, Rust, and .NET tooling but zero Ruby support. Ruby test and build output is just as verbose as the ecosystems already supported.

Requested commands

rspec (highest value)

rtk rspec -- filter test output to show only failures and the summary line. rspec's default formatter is already pretty good, but the full output on large suites includes passing test names, pending tests, and seed info that aren't useful in an LLM context.

rake

rtk rake -- filter task output. Rake is verbose about task invocation tracing when run with --trace, and build output can be noisy.

bundler

rtk bundle -- filter bundle install / bundle update output. Most of the output is "Using gem_name x.y.z" lines that aren't useful; only changes (Installing/Removing) and errors matter.

rails (nice to have)

rtk rails -- filter rails test, rails console output, migration output, etc.

Prior art

The Python ecosystem support (rtk pytest, rtk ruff, rtk pip) is a good model for how these could work -- same pattern of stripping noise and surfacing failures/changes.