[DAR-7975] Fix Linux AArch64 packaging for upolygon

[assemkozhekova]

Summary

• include Cython .pyx and .pxd sources in source distributions
• bump upolygon to 0.2.3
• build Linux AArch64 wheels with cibuildwheel and QEMU
• use explicitly signed contour labels for consistent AArch64 behavior
• run wheel tests through cibuildwheel
• build, install, and test the sdist in an isolated environment in PR and release CI

Context

upolygon 0.2.2 has no Linux AArch64 wheel and its sdist omits the .pyx sources selected under PEP 517 build isolation. This causes installs such as darwin-py 3.6.0 on Python 3.13/Linux AArch64 to fail with ValueError: 'upolygon/draw_polygon.pyx' doesn't match any files.

ARM64 validation also exposed that plain char contour labels interpreted the -1 sentinel as unsigned, producing an incorrect inner contour. The labels now use signed char explicitly.

Validation

• confirmed the 0.2.3 sdist contains all four .pyx extension sources
• PR CI passes on Python 3.10, 3.11, 3.12, and 3.13
• isolated sdist CI passes
• built a candidate wheel and sdist under Linux AArch64/Python 3.13.15
• installed darwin-py==3.6.0 with both the candidate wheel and forced sdist
• pip check passes in both clean AArch64 environments
• all 24 tests pass for both artifacts on AArch64

  

[linear-code]

DAR-7975

[vvihorev]

Looks good