Bump mypy minimum to 1.19, regenerate lock file, clean up dead version checks

- Bump mypy version constraint from >=1.12,<1.21 to >=1.19,<1.21
- Regenerate poetry.lock to fix CI (lock file was out of sync)
- Remove dead version-check code for mypy < 1.16 in plugin
  (analyze_member_access msg parameter handling no longer needed)
- Remove unused imports (importlib.metadata.version, typing.Any)

Agent-Logs-Url: https://github.com/dry-python/returns/sessions/ec3a5de7-f5a3-49a4-a973-9265d6a4555e

Co-authored-by: sobolevn <4660275+sobolevn@users.noreply.github.com>

Author: Copilot