## Summary
Previously, we wouldn't respect configuration files in directories
_above_ a workspace root. But this is somewhat problematic, because any
`pyproject.toml` will define a workspace root...
Instead, I think we should _start_ the search at the workspace root, but
go above it if necessary.
Closes: #5929.
See: https://github.com/astral-sh/uv/pull/4295.
## 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`.
