Release 1.27.1

What's New

A maintenance release folding in fixes and cleanup that had accumulated on the
development branch. No public API changes.

Bug Fixes

• Message accumulator no longer throws on unmatched message kinds. A missing
  fallthrough in Messages.Accumulator.add could raise a MatchError when a
  message kind wasn't explicitly handled; a default no-op case now makes it
  robust.
• GBNF grammar is now parseable by llama.cpp. The EBNF→GBNF converter was
  emitting escapes llama.cpp's GBNF parser rejects (\/ and \. carried into
  char classes/literals, and single-quoted EBNF literals passed through). The
  converter now strips GBNF-invalid backslash escapes, unescapes non-special
  literals, and converts single-quoted literals to double-quoted GBNF. The
  generated riddl-grammar.gbnf was regenerated and passes the validator (all
  258 rules).

Improvements

• Code cleanup for issues flagged by SonarQube in CommonOptionsHelper,
  Messages, and ResolutionPass — simpler, clearer code with no behavior
  change.

Internal

• Upgraded GitHub Actions versions in the Scala CI workflow to clear
  deprecation warnings.
• Removed an unneeded documentation test suite (CheckDocsTest).