Add `uv sync --script` (#11361)
## Summary
The environment is located at a stable path within the cache, based on
the script's absolute path.
If a lockfile exists for the script, then we use our standard lockfile
semantics (i.e., update the lockfile if necessary, etc.); if not, we
just do a `uv pip sync` (roughly).
Example usage:
```
❯ uv init --script hello.py
Initialized script at `hello.py`
❯ uv add --script hello.py requests
Updated `hello.py`
❯ cargo run sync --script hello.py
Using script environment at: /Users/crmarsh/.cache/uv/environments-v1/hello-84e289fe3f6241a0
Resolved 5 packages in 3ms
Installed 5 packages in 12ms
+ certifi==2025.1.31
+ charset-normalizer==3.4.1
+ idna==3.10
+ requests==2.32.3
+ urllib3==2.3.0
```
Closes https://github.com/astral-sh/uv/issues/6637.
