[NEW]: Upgrade to Cython 3.1.3

[FIX]: Include .pxd files in the source .tar.gz

[FIX]: Don't require pip, it's not needed

[FIX]: Add back some import compat for backtrader

[FIX]: Silence project.license warnings when building.

[FIX]: Fix regression in abstract function parameters not coercing integers

[FIX]: Support PEP-517 style installation

[NEW]: Upgrade to Cython 3.1.2

[NEW]: Build binary wheels for Windows, macOS, and Linux.