fix(python): pin python version and add uv caching

[slbotbm]

While working on the python sdk, often uv sync --all-extras does not actually recreate the .so file using the latest changes and leaves the old version of the sdk, leading to difficulties in actually testing it on local. This change adds explicit cache keys for files. If the files are changed, the .so extension is automatically rebuilt on running uv sync --all-extras. (caveat: it will also be run when running other commands like uv run ruff format since there is a hidden sync step in these commands).

I also pin the python version to 3.10 explicitly. Previously, we only declare the python version to be >= 3.10, which led to uv downloading python according to the following hierarchy:

1. Existing compatible uv-managed Python, preferring newer versions.
2. First compatible system Python found—not necessarily newest.
3. If none exists, downloads the latest compatible stable Python.

By pinning the version, we force uv to utilize 3.10.

[slbotbm]

/ready

[ryankert01]

We can add these 3 .python-version files to current sync check (sync-python-interpreter-version.sh) so precommit would detect version inconsistencies if we upgrade at somewhere.

[slbotbm]

@ryankert01 updated, thanks for the reminder.