Deprecate the --isolated flag (#5466)

## Summary

This PR deprecates the `--isolated` flag. The treatment varies across
the APIs:

- For non-preview APIs, we warn but treat it as equivalent to
`--no-config`.
- For preview APIs, we warn and ignore it, with two exceptions...
- For `tool run` and `run` specifically, we don't even warn, because we
can't differentiate the command-specific `--isolated` from the global
`--isolated`.

.github/workflows/sync-python-releases.yml

@@ -20,8 +20,8 @@ jobs:
       - uses: hynek/setup-cached-uv@v2
       - name: Sync Python Releases
         run: |
-          uv run --isolated -- fetch-download-metadata.py
-          uv run --isolated -- template-download-metadata.py
+          uv run -- fetch-download-metadata.py
+          uv run -- template-download-metadata.py
         working-directory: ./crates/uv-python
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}