## Summary
Updates the `--python` flag to accept Python executables in virtual
environments. Notably, we do not query the executable and it _must_ be
in a canonical location in a virtual environment. This is pretty naive,
but solves for the trivial case of `ty check --python .venv/bin/python3`
which will be a common mistake (and `ty check --python $(which python)`)
I explored this while trying to understand Python discovery in ty in
service of https://github.com/astral-sh/ty/issues/272, I'm not attached
to it, but figure it's worth sharing.
As an alternative, we can add more variants to the
`SearchPathValidationError` and just improve the _error_ message, i.e.,
by hinting that this looks like a virtual environment and suggesting the
concrete alternative path they should provide. We'll probably want to do
that for some other cases anyway (e.g., `3.13` as described in the
linked issue)
This functionality is also briefly mentioned in
https://github.com/astral-sh/ty/issues/193
Closes https://github.com/astral-sh/ty/issues/318
## Test Plan
e.g.,
```
uv run ty check --python .venv/bin/python3
```
needs test coverage still
