Allow snapshots to be updated from failures in CI (#18424)
Persists snapshots as artifacts on test failure in CI and adds a script
to apply them locally
```
❯ ./scripts/apply-ci-snapshots.sh
Found pull request #18424 for branch 'zb/ci-snapshots'...
Found latest CI run 23022983761
Downloading pending snapshot artifacts...
Downloaded 3 artifacts
Applying 2 snapshot changes...
accepted:
crates/uv/tests/it/pip_install.rs:13679 (transitive_dependency_config_settings_invalidation-2)
crates/uv/tests/it/python_install.rs:1694 (python_install_default-5)
```
We infer the target run via the `gh` CLI. You may also provide the run
ID directly.
We'll merge snapshot artifacts from multiple platforms, so if there are
platform-specific failures on both Linux and Windows we'll apply both.
