fix(extract): warn when files are skipped due to a missing optional dependency (#1745)

[rithyKabir]

Fixes #1745.

Problem

When the [sql] extra isn't installed, extract_sql returns an "error" result for every .sql file — and nothing consumes it. Both existing safety nets deliberately miss this case:

• the Ruby: stable subset of files yields zero nodes in full-repo runs (0.9.6) — each extracts fine in isolation #1666 zero-node warning skips any result carrying an error
• the R (.r/.R) listed in CODE_EXTENSIONS but has no AST extractor — silently drops all R files with zero warning #1689 no-extractor warning only covers extensions with no dispatch entry, and .sql has one

So the graph builds "successfully" while the entire SQL schema silently contributes nothing. The same mechanism affects the other optional grammars that hard-fail on import: .tf/.tfvars/.hcl ([terraform]) and .dm/.dme ([dm]). Pascal is unaffected — it falls back to its regex extractor.

Fix

extract() now surfaces these files right after the #1689 block, grouped by extension, naming the extra that restores the language:

warning: 2 .sql file(s) contributed nothing to the graph because a dependency is missing: tree_sitter_sql not installed. Install it with: pip install "graphifyy[sql]" (#1745)

A new _EXTRA_FOR_EXTENSION map lives next to _DISPATCH so the two stay in sight of each other. For a missing core grammar (broken env), the extension isn't in the map and the extractor's own error is printed verbatim with no extra hint.

Tests

Mirrors the #1689 regression tests: one simulates the missing dependency (monkeypatch.setitem(sys.modules, "tree_sitter_sql", None)) and asserts the warning fires while a sibling .py file still extracts normally; one asserts no warning when the extra is installed. Full tests/test_extract.py passes (117/117), ruff clean.

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