Fix missing BPE vocabulary asset in non-editable install

[claydugo]

Minimal Reproducer

pip install git+https://github.com/facebookresearch/sam3.git
python -c "
import os, sam3
bpe_path = os.path.join(os.path.dirname(sam3.__file__), '..', 'assets', 'bpe_simple_vocab_16e6.txt.gz')
print(f'Path: {bpe_path}')
print(f'Exists: {os.path.exists(bpe_path)}')  # False

https://github.com/facebookresearch/sam3/blob/84cc43bca4347b772f17/sam3/model_builder.py#L584

Including #167 in here as its required but we are applying that patch in the feedstock already.

This would PR would help us package for conda-forge.

[claydugo]

Applied to the conda-forge package in conda-forge/sam3-feedstock#2

[claydugo]

Fixed in #327