add tss api to ffi crate

[Person-93]

Adds tss api from pythread.h to the ffi crate.

https://github.com/python/cpython/blob/49f96670d98c50eca769dd3f6fb5b6de11010617/Include/pythread.h#L106-L121

[codspeed]

Merging this PR will not alter performance

✅ 141 untouched benchmarks
⏩ 6 skipped benchmarks¹

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_{Comparing Person-93:ffi-tss (c27fa1e) with main (4b642bc)}

Footnotes

1. 6 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

[davidhewitt]

Thanks!