feat: generate features from source via [tool.testmap.generate]

[tylerriccio33]

What

Adds [[tool.testmap.generate]], which derives the expected feature universe statically from source. A feature with zero tests previously didn't exist in testmap's model — it only appeared once a test tagged it. Now generated features surface as all-missing rows, closing that blind spot.

Each block is a small select / from / where query:

[[tool.testmap.generate]]
select = "functions"   # "functions" or "classes"
from = "src/**/*.py"    # glob (Linux rules, ** allowed), relative to pyproject.toml
where = "public"        # "public" | "private" | "all" (default)

• Top-level defs only (a file's public API); feature name = symbol name.
• Multiple blocks combine and dedupe.
• Resolved at load_config time and seeded into the matrix, so both the CLI and the pytest plugin get it with no call-site changes.
• Zero new dependencies — built on the stdlib ast already used by discover.py.

Known tradeoff

Feature names are symbol-derived, so renaming a symbol silently orphans its tests. Inherent to any glob/query-based derivation; the refactor-safe fix is an in-source @feature decorator, left for a follow-up.

Testing

make lint, make test (33 passed), make prek (incl. testmap self-check) all green. New tests cover kind/visibility selection, recursive globbing + dedupe, unknown-select rejection, and end-to-end config generation. README documented with a worked example.

🤖 Generated with Claude Code