Remove adjacent imports replaced by plain functions

[x0Lazarus]

Addresses #321 by handling an F811 import immediately followed by a plain function that replaces the same binding. For example, from autoflake import fix_code before def fix_code(): ... can now be removed with --remove-all-unused-imports or --imports=autoflake.

The new rule requires a single imported name and consecutive statements in a module or function body. It preserves decorators, defaults, annotations, type parameters, class bodies, ambiguous same-line imports, and the __builtins__/__name__ bindings that function creation can read. Existing import-selection, comment, and __init__ filters still apply. Adjacency is checked during each filtering pass, including after existing cleanup removes a redundant pass.

Validation on Python 3.12 / Windows:

• The final regression tests reproduce 15 failing subcases on unchanged main; the complete suite passes with 190 tests and 52 subtests under both Pyflakes 3.4.0 and the supported minimum 3.0.0.
• Existing fuzz checks pass in both modes; wheel/sdist builds and wheel-import smoke checks pass.
• All seven pre-commit hooks pass with ty targeting Linux. Native Windows ty retains the same two diagnostics as unchanged main (worker_count and signal.SIGPIPE). Hosted and other Python-version checks have not run locally.