Support creating a free-threaded environment

[ngoldbaum]

Perhaps complicated by the fact that hatch isn't easily installable on the free-threaded build (#1801, but see https://github.com/pypa/hatch/issues/1801#issuecomment-2715720577), it doesn't look like it's possible to create a hatch environment with a free-threaded interpreter:

$ hatch python install 3.13t
Unknown distributions: 3.13t

Is that something that you'd be interested in adding support for?

I think if we do, projects should be able to install hatch in a GIL-enabled interpreter, and then use hatch to orchestrate downloading a free-threaded interpreter and using it to run tests, sidestepping #1801.