## Summary
As described in https://github.com/astral-sh/uv/issues/12229, `pip
install` with `--target` or `--prefix` seem like they should install the
necessary python version if it doesn't exist, but they currently don't.
Most minimal reproduction is something like:
```
> uv python uninstall 3.13
...
> uv pip install anyio --target target-dir --python 3.13
error: No interpreter found for Python 3.13 in virtual environments, managed installations, or search path
```
This also fails without `--target`, but a venv is expected in that case,
so the with `--target`/`--prefix` is the only version that needs to be
fixed. The same mechanism occurs for `uv pip sync` as well.
## Test Plan
Added tests for install and sync that failed before fix and now pass.
---------
Signed-off-by: Mikayla Thompson <mrt@mikayla.codes>
Mikayla Thompson
88811553e4