refactor(testing): attach filler plugin state via typed StashKeys

[tcoratger]

Motivation

The fill pytest plugin smuggled five attributes onto the pytest.Config object — the fixture collector, the selected fork class, and the per-test fixture path (absolute + relative) and format. Each write needed a # type: ignore[attribute-defined] (six in total), and each read used a hasattr(...) probe:

config.fixture_collector = FixtureCollector(...)   # type: ignore[attribute-defined]
config.test_fork_class = fork_class                # type: ignore[attribute-defined]
...
if hasattr(config, "test_fork_class"):
    fork_class = config.test_fork_class

This is monkey-patching the config with undeclared attributes — untyped, unchecked, and flagged by the type checker.

What this does

Stores the same state in config.stash, keyed by module-level StashKeys — the documented, type-safe mechanism for plugin state:

FIXTURE_COLLECTOR_KEY: pytest.StashKey[FixtureCollector] = pytest.StashKey()
TEST_FORK_CLASS_KEY: pytest.StashKey[type[BaseFork]] = pytest.StashKey()
FIXTURE_PATH_ABSOLUTE_KEY: pytest.StashKey[str] = pytest.StashKey()
FIXTURE_PATH_RELATIVE_KEY: pytest.StashKey[str] = pytest.StashKey()
FIXTURE_FORMAT_KEY: pytest.StashKey[str] = pytest.StashKey()

Result:

• All six type: ignores removed. The collector reads back as FixtureCollector and the fork class as type[BaseFork] — fully typed.
• All hasattr probes replaced with KEY in config.stash.
• The fork class is resolved by membership + direct indexing (FORKS_BY_NAME[name]) so it is never Optional — the type checker does not narrow through the NoReturn CLI exit, and this keeps fork_class.name() / <= valid without an assert.

No behavior change: same data flow, same fixture output, same fork filtering and CLI error paths.

Testing

• just check passes (lint, format, ty, codespell, mdformat) — zero type: ignore, zero hasattr(config...) left in the file.
• Fill smoke: 118 SSZ fixtures generate and write to disk via the stashed collector; report paths attach correctly.
• Invalid --fork still exits cleanly with the same message and lists available forks.

🤖 Generated with Claude Code