Fix Ruby grammar conformance gaps

[tarebyte]

Summary

• Fix scanner ambiguity around heredocs, operators, percent literals, regexes, Unicode symbols, and comments.
• Fix lambda boundaries, ranges, parenthesized returns, endless method command bodies, and declaration comment ownership.
• Add pinned Prism/ruby-spec conformance coverage, recursively parse CI examples, and clear the valid-Ruby allowlist.
• Update to Tree-sitter 0.26.13 while preserving parser ABI 14.

References

• Fixes Nested heredocs are not parsed correctly #148, fixes Block comment terminator edge case #203, fixes bug: String concatenation using << and without spaces considers it as a heredoc #256, and fixes bug: leading method comment is outside method body #272.
• Fixes Parse error in block argument with space after & #218, fixes Syntax error in one line def with a command call as right-hand side #242, fixes Parse error in anonymous block arguments #244, fixes bug: Unary plus should parse the same way as unary minus. #281, and fixes bug: Parser error when forwarding an anonymous block to another function without surrounding with parenthesis (ampersand &) #290.
• Fixes bug: accepting incorrect syntax: return(1, 2). #280, fixes bug: escape sequences inside regular expressions are not treated as part of regular expressions #284, and fixes bug: Some multi-byte Unicode characters are not highlighted #292.
• Partially addresses bug: accepting incorrect syntax #275 by fixing endless-range continuation; bool = not true remains accepted because it is valid Ruby.
• Reimplements Endless method command #202, fix: parse regexps with character classes as string_content #285, Allow for more valid method calls with block arguments #291, Fix Unicode symbol scanning #293, Reject multiple values in parenthesized return #294, and Support percent string equals delimiter #295, plus the endless-method, return, and range portions of add some important features from ruby > 3.0 and solve some issue #282.
• Incorporates the setup-action update from Update tree-sitter/setup-action/cli to try to fix CI #288 and the generated array.h refresh from Sync vendored array.h to the tree-sitter 0.26.4+ template #298.

Validation

• 326 corpus and highlight tests
• 4,431 Prism-valid ruby/spec files with zero mismatches
• 4,433 recursively parsed example files

[tarebyte]

Sorry this was meant for my fork for testing.