Add CHAFA_SYMBOL_TAG_OCTANT support

[kappa]

Chafa added built-in octant support in Nov 2024, which landed in the 1.16.0 release. Octants are 2×4 binary mosaic characters — 256 patterns per cell, a significant step up from sextants (64 patterns) for terminal image rendering.

Since chafapy's CI builds against chafa master, a new release would pick up the octant glyph bitmaps in the bundled libchafa.so. The Python-side change is just adding the enum value to src/chafa/enums.py:

CHAFA_SYMBOL_TAG_OCTANT = (1 << 26)
(Matching the C definition in chafa-symbol-map.h)

Thank you for the excellent bindings!