Rename package directory from fmpose to fmpose3d

[Copilot]

Completes the FMPose → FMPose3D rebranding by renaming the Python package directory and updating all references.

Directory rename:

• Renamed fmpose/ to fmpose3d/ using git mv to preserve history (64 files)

Import path updates:

• Updated all import statements from fmpose.* to fmpose3d.* across scripts, tests, and demos
• Modified files: scripts/FMPose3D_main.py, animals/scripts/main_animal3d.py, demo/vis_in_the_wild.py, tests/*.py, and internal package imports

Configuration updates:

• Updated pyproject.toml version attribute: fmpose.__version__ → fmpose3d.__version__
• Updated README.md installation instructions to reference fmpose3d package name

Example change:

# Before
from fmpose.common import opts, Human36mDataset, Fusion
from fmpose.models import Model as CFM

# After
from fmpose3d.common import opts, Human36mDataset, Fusion
from fmpose3d.models import Model as CFM

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