feat(treesitter): add go AST rules and standardized testdata

[HarshK97]

Problem

1. Go AST rules were sitting inside internal/treesitter/rules.yml with global defaults instead of having their own config folder.
2. The test fixtures under tests/testdata/ had messy, unstandardized folder names and old test files that clogged test runner output.
3. Adding new test fixtures was triggering the CI benchmark workflow even when no benchmarked code changed.

What Changed

• Extracted Go AST normalization rules into internal/treesitter/go/rules.yml and cleaned up rule loading in internal/treesitter/rules.go.
• Renamed and organized Go test cases under tests/testdata/go_gin_*, regenerated golden expectations, and removed outdated fixture folders(AI is quite good at s̶t̶e̶a̶l̶i̶n̶g̶ borrowing Open Source Codebase lol).
• Added path filtering to .github/workflows/ci.yml so benchmark runs don't trigger on testdata changes.