[sorinc03]

Summary

GatherExportsVisitor ignores literal __all__.append() and .extend() calls. Consequently, RemoveUnusedImportsCommand can delete an import that the module explicitly exports through one of those calls.

Recognize direct, unconditional module-level expression statements using literal strings or literal list/tuple additions. Structural receiver checks exclude indirect call/subscript receivers, and module-level call indexing excludes deferred/conditional expressions. Existing assignment gathering is preserved.

Refs #1481. This implements literal additions; removal remains conservative because unresolved additions or aliases can leave duplicate exported names. The full issue should remain open for sound removal analysis.

Test Plan

• Against unchanged base, the two final regression methods fail in ten subcases covering missing export gathering and incorrectly deleted imports.
• Final focused visitor/codemod tests: 28 pass.
• Real RemoveUnusedImports regressions retain exported imports and preserve imports around unresolved additions/removals, aliases, conditionals, functions, lambdas and generators.
• Full uv run poe test: 2,167 tests, no unexpected failures; 14 skips and two expected failures. Coverage 95.8%.
• uv run poe format, uv run poe lint and uv run poe typecheck pass; diff check clean.
• Python 3.11 with the repository's locally built Rust/native parser; no Rust source changes. Wider Python/platform matrix remains for CI.