fix: pass :python option from config to uv fetch/init

The :python option (e.g., "3.14t" for free-threaded builds) was read
from Application.compile_env but never forwarded to Pythonx.Uv.fetch/3
or Pythonx.Uv.init/3. This caused uv to download the regular Python
build instead of the free-threaded variant.

Author: AJReade

lib/pythonx/application.ex

@@ -26,7 +26,8 @@ defmodule Pythonx.Application do
   uv_init_env = Application.compile_env(:pythonx, :uv_init)
   pyproject_toml = uv_init_env[:pyproject_toml]
   uv_version = uv_init_env[:uv_version] || Pythonx.Uv.default_uv_version()
-  opts = [uv_version: uv_version]
+  python = uv_init_env[:python]
+  opts = [uv_version: uv_version, python: python]
 
   if pyproject_toml do
     Pythonx.Uv.fetch(pyproject_toml, true, opts)