fix: correctly set UV_PYTHON to the wrapped python interpreter

[mauricege]

Underlying Issue
Since #1959, UV_PYTHON is forced to devenv's python interpreter. However, it is the unwrapped interpreter. This of course breaks the native libs functionality.

To reproduce
Create a devenv.nix with languages.python.uv.sync.enable = true:

{ pkgs, config, inputs, ... }:
{
  languages.python = {
    enable = true;
    venv.enable = true;
    uv = {
      enable = true;
      sync.enable = true;
    };
  };
}

Check UV_PYTHON variable from shell:

echo $UV_PYTHON
> /nix/store/fqm9bqqlmaqqr02qbalm1bazp810qfiw-python3-3.12.9/bin/python3.12 <- This is an unwrapped interpreter

Fix
Just use the wrapped python bound to package in python.nix