Blender extension on mhp-formats and mhfu-port

[sp00ktober]

The research Blender addon becomes a Blender 4.2+ extension in apps/blender (GPL-3.0-or-later), on mhp-formats and mhfu-port. For sp00ktober/MHFU-ModKit#70.

• Extension (mhfu_blender):
  • Import: an MHFU model PAC, a built port, or an MHP3rd model with its emNNN moveset.
  • Export as an MHFU PAC, and push it into the memory stick's inject folder.
  • Animation: bones rest unrotated, so an Action's channels are the engine's. Edited clips are written back through motion.put; unedited ones stay byte for byte.
  • Geometry: groups are written in place while their topology holds and rebuilt otherwise; UV seams split.
  • The re-skin, in-game-anim and port operators are dropped: a manifest does those.
• Packaging: uv run apps/blender/build.py stages the version and the wheels from uv.lock, then runs extension build and validate.
  • Pure-Python wheels only, so one zip serves every OS; numpy is Blender's own.
  • build.py test installs the zip into a throwaway profile and runs apps/blender/tests inside Blender. CI has no Blender, so those tests skip there.
• mhfu-port:
  • numpy>=1.24 (Blender 4.2 to 5.0 bundle 1.24 or 1.26).
  • mhfu_port.model is the studio's loader, now shared. It stays free of mhfu, and a test enforces that.
  • motion.put is the inverse of fk.rig_clip.
  • fk.Curves now uses the engine's cubic spline with the key eases (EU 0x088630D0) instead of linear interpolation. Between keys, linear was off by up to ~430 units.
    • Built ports are byte-identical before and after.
    • verify's tear and stretch figures move a little.
    • Four studio goldens are regenerated; two of them were already stale on main.
• mhp-formats: quantize_weights makes a vertex's weights sum to 128, as native data does. Built ports are unchanged.
• mypy: native_parser = true, because the bpy stubs use 3.12 generics. mypy calls this option experimental.

The issue's bugs:

1. Multi-group PMO export now goes through Pmo.to_bytes.
   2, 4, 6, 7. Geometry, skeletons, textures and vertex scale are fixed by the shared loader.
2. Pmo.material is confirmed by render. The 284 unexplained groups were the old walker's 0x20 stride reading Khezu and Red Khezu group records as a fifth mesh.
3. The moveset is an explicit input.
4. The port operator is gone.

Tested:

• pytest with game data: everything passes; studio 701 passed offscreen.
• Inside Blender: 40 passed on 4.2.23 and 4.5.3; 39 passed and 1 skipped on 5.2.2 (the skip is the test for the pre-4.4 Action API).
• The installed zip round-trips the Tigrex and the brute_tigrex and zinogre builds byte for byte on all three Blenders.
• All 101 MHFU model PACs export byte-identical.
• ruff, strict mypy and pre-commit pass.
• Not tested: a push into a running game.

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