In addition to our flake catch, keep a snapshot.

Extends #13817

See #14160

Same as #13817

This fixes an obscure cache collision in Python interpreter queries,
which we believe to be the root cause of CI flakes we've been seeing
where a project environment is invalidated and recreated.

This work follows from the logs in [this CI
run](https://github.com/astral-sh/uv/actions/runs/15934322410/job/44950599993?pr=14326)
which captured one of the flakes with tracing enabled. There, we can see
that the project environment is invalidated because the Python
interpreter in the environment has a different version than expected:

```
DEBUG Checking for Python environment at `.venv`
TRACE Cached interpreter info for Python 3.12.9, skipping probing: .venv/bin/python3
DEBUG The interpreter in the project environment has different version (3.12.9) than it was created with (3.9.21)
```

(this message is updated to reflect #14329)

The flow is roughly:

- We create an environment with 3.12.9
- We query the environment, and cache the interpreter version for
`.venv/bin/python`
- We create an environment for 3.9.12, replacing the existing one
- We query the environment, and read the cached information

The Python cache entries are keyed by the absolute path to the
interpreter, and rely on the modification time (ctime, nsec resolution)
of the canonicalized path to determine if the cache entry should be
invalidated. The key is a hex representation of a u64 sea hasher output
— which is very unlikely to collide.

After an audit of the Python query caching logic, we determined that the
most likely cause of a collision in cache entries is that the
modification times of underlying interpreters are identical. This seems
pretty feasible, especially if the file system does not support
nanosecond precision — though it appears that the GitHub runners do
support it.

The fix here is to include the canonicalized path in the cache key,
which ensures we're looking at the modification time of the _same_
underlying interpreter.

This will "invalidate" all existing interpreter cache entries but that's
not a big deal.

This should also have the effect of reducing cache churn for
interpreters in virtual environments. Now, when you change Python
versions, we won't invalidate the previous cache entry so if you change
_back_ to the old version we can re-use our cached information.

It's a bit speculative, since we don't have a deterministic reproduction
in CI, but this is the strongest candidate given the logs and should
increase correctness regardless.

Closes #14160
Closes #13744
Closes #13745

Once it's confirmed the flakes are resolved, we should revert

- #14275
- #13817