#25345 [ruby-nextgen] Sanitize literal path segments when deriving action method names (#24998)

Fixes #24998

In RubyApiRouting#deriveAction, literal path segments containing embedded {param} placeholders (such as {id}!preview or {id}:archive) or punctuation characters (such as . in export.csv, which StringUtils.underscore converts into /) were passed directly to underscore(...), generating invalid Ruby method definitions (def {id}!preview, def {id}:archive, def export/csv).

Changes

• Strip {...} parameter placeholders and replace non-identifier characters with _ in RubyApiRouting#deriveAction before calling underscore(...).
• Add unit tests in RubyApiRoutingTest.

PR checklist

• Read the contribution guidelines.
• Existing ruby-nextgen samples (bin/configs/ruby-nextgen.yaml, bin/configs/ruby-nextgen-qdrant.yaml) are unaffected.
• Mention Ruby technical committee members: @cliffano @zlx @autopp @n-rodriguez

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Summary by cubic

Fixes #24998. Sanitizes literal path segments in ruby-nextgen route derivation so embedded {param} placeholders and punctuation no longer produce invalid Ruby method names (e.g. export.csv became export/csv). Now strips placeholders and replaces non-identifier characters with underscores before deriving the action name.