`main_thread_forkserver` doesn't actually need py3.14
`concurrent.interpreters` (PEP 734) — it forks from a
non-trio worker thread and runs `_trio_main` in the child,
same shape as `trio_proc`. The previous `_has_subints`
gate + subint-family `case` arm were a copy-paste error.
In `tractor.spawn._main_thread_forkserver`,
- drop the `_has_subints` import + the `RuntimeError`
raise in `main_thread_forkserver_proc()`.
- drop the now-unused `import sys` (only used by the
prior error msg).
In `tractor.spawn._spawn.try_set_start_method()`,
- pull `'main_thread_forkserver'` out of the subint-
family arm (which still gates on `_has_subints`).
- merge it into the `'trio'` arm — both set `_ctx = None`
bc neither needs an `mp.context`.
(this commit msg was generated in some part by [`claude-code`][claude-code-gh])
[claude-code-gh]: https://github.com/anthropics/claude-code
(cherry picked from commit fc5e80fea5)
Gud Boi
c358ad7837