chore: EOL python below python 3.10 (#2666)
* chore: require Python 3.10+ across Cog
Set minimum Python version to 3.10 in config validation, dockerfile base logic, and CI/test matrices.
Update txtar fixtures (apt_packages, bad_dockerignore, torch base image tests, setup_subprocess_multiprocessing) to use python_version: 3.10 and allow coglet-rust runs.
Add python38_deprecated + python39_deprecated integration tests and remove optional_input.txtar (Optional+Input default behavior).
Tighten AST helpers and migration logic for 3.10+ parsing behavior.
* test: unskip rust/dataclass for cuda baseimage
* fix: filter torch packages below py3.10
