Sanity checks free threading compatibility

[greateggsgreg]

This adds sanity checks for filesystem inputs based on static analysis and dynamic fuzzing.

Also add support for free-threaded Python

[joachimmetz]

Thanks for the suggested changes, though it looks like there are some cross-platform compatibility issues

[greateggsgreg]

Thanks for the suggested changes, though it looks like there are some cross-platform compatibility issues

The mutex header includes ends up including limits.h, but our misc.h redefines min & max. These are almost certainly in modern platforms as we already have to require a C++14 compiler. Removed the redefinitions of min & max in misc.h.

Tested on local Linux machine (originally was developing on Windows) and works fine.

[joachimmetz]

LGTM