Wheels for CPython 3.15 and free-threaded 3.15t

[bdbarnett]

Python 3.15.0 came out on 2026-10-09. This adds pydevices-lvgl wheels for it, standard and free-threaded (3.15t), on Linux x86_64 and Windows AMD64. Android and Pyodide stay at cp313/cp314.

cibuildwheel==4.2.1 --print-build-identifiers now lists cp311–cp315 plus cp315t on Linux and on Windows, four Android wheels and two Pyodide ones: four more wheels in all.

Tested before merging, because pull-request CI doesn't run cibuildwheel:

• Linux: a temporary workflow on this branch, since removed, built both cp315 wheels with cibuildwheel 4.2.1. Both passed auditwheel repair, and both passed the import test (import lvgl; lv.init(); lv.deinit()).
• Windows: both wheels built locally with MSVC against the python.org 3.15.0 installers. Each passed the same test three times.

Unlike cp314, 3.15 doesn't segfault at shutdown, so it keeps its import test. The 3.15t wheel loads with the GIL turned back on, because the module doesn't declare Py_mod_gil yet.