Support pre-releases in Python version requests - `command --python <…

…major.minor.pre-release>` (#7335)

## Summary

This PR adds support to include Python pre-releases when requesting
versions.
Check out the docs for commands that support the `Python` option: 
```text
--python, -p python
The Python interpreter to use for the virtual environment.
```
At least the following scenarios are supported:
```bash
3.13.0a1
3.13b2
3.13rc4
313rc1
```

## Test Plan

I added a basic unit test to `uv/crates/uv-python/src/discovery.rs`. I
could have added more, but I have not discovered any relevant places.

CI passes

Note: I was unable to execute the entire test set locally. There were at
least some timeout issues (some tests took over 60 seconds).

========== output ===========
beta version
```bash
cargo run -- venv --python 3.13.0b3                                                                                                           ░▒▓ 94% 󰁹
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.20s
     Running `target/debug/uv venv --python 3.13.0b3`
Using Python 3.13.0b3 interpreter at: /home/mikko/.pyenv/versions/3.13.0b3/bin/python3
Creating virtualenv at: .venv
Activate with: source .venv/bin/activate
````
release candidate
```bash
 cargo run -- venv --python 3.13.0rc2                                                                                                          ░▒▓ 94% 󰁹
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.83s
     Running `target/debug/uv venv --python 3.13.0rc2`
Using Python 3.13.0rc2 interpreter at: /home/mikko/.pyenv/versions/3.13.0rc2/bin/python3
Creating virtualenv at: .venv
Activate with: source .venv/bin/activate
```

```bash
cargo run -- venv --python 313rc2                                                                                                             ░▒▓ 94% 󰁹
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.31s
     Running `target/debug/uv venv --python 313rc2`
Using Python 3.13.0rc2 interpreter at: /home/mikko/.pyenv/versions/3.13.0rc2/bin/python3
Creating virtualenv at: .venv
Activate with: source .venv/bin/activate
```

---------

Co-authored-by: Zanie Blue <contact@zanie.dev>