[sys] Add the 3.14 _jit 'module'

[lambda-abstraction]

Type annotations for sys._jit
To handle the fact that it is a module despite not being importable, i adopted the approach used for sys.monitoring from #10890

[github-actions]

Diff from mypy_primer, showing the effect of this PR on open source code:

pandas (https://github.com/pandas-dev/pandas)
- pandas/core/computation/ops.py:328: error: Need type annotation for "_binary_ops_dict" (hint: "_binary_ops_dict: dict[<type>, <type>] = ...") [var-annotated]

[JelleZijlstra]

I'm a bit suspicious about the mypy-primer hit, as it seems unrelated to the PR; maybe there's a nondeterminism bug in mypy. I'll investigate that some more.

[srittau]

I'm a bit suspicious about the mypy-primer hit, as it seems unrelated to the PR; maybe there's a nondeterminism bug in mypy. I'll investigate that some more.

We've seen the same primer hit in other PRs. So there's certainly some weirdness, but unrelated to this PR.

[JelleZijlstra]

I had Codex look at it and I think it figured it out, I'll send a PR to mypy once I confirm.