Add AST-grep lint foundations

[edmundmiller]

Stack root.

Adds the AST-grep helper, parser dependency setup, parser availability tests, and migration status script. Rule migrations live in child PRs.

Base: dev

Stack

1. Bump tree-sitter-nextflow parser pin #4378
2. Add AST-grep lint foundations #4377 👈 current
3. Migrate pipeline lint rules to AST-grep #4381
4. Flag legacy versions.yml topic outputs #4379
5. Flag legacy versions emits #4380

[codecov]

Codecov Report

❌ Patch coverage is 30.92784% with 67 lines in your changes missing coverage. Please review.
✅ Project coverage is 77.81%. Comparing base (e1cf743) to head (9500344).

Files with missing lines	Patch %	Lines
nf_core/astgrep.py	30.92%	67 Missing ⚠️

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