Investigate `gh-pages` impact on full clone size and time

Description

A local controlled file:// clone experiment suggests that gh-pages is substantially inflating normal full-clone cost for NVIDIA/cuda-python.

Measured clone times:

• With gh-pages: 47.44 seconds
• Without gh-pages: 1.79 seconds

Measured size estimates from the same experiment:

• With gh-pages: .git size about 1.2G
• Without gh-pages: .git size about 38M
• Estimated reduction: about 1.19 GB by filesystem size, or about 1.17 GB by Git object disk-usage accounting

Full measurement details and evidence are in:

• https://github.com/NVIDIA/cuda-python/issues/2190#issuecomment-4672575628

For initial solution exploration, start from:

• https://github.com/NVIDIA/cuda-python/issues/2190#issuecomment-4673051307

Additional real-world measurements from two NVIDIA-internal wired-network machines (see comments below for details):

In both runs, the normal clone fetched about 693k packed objects and 1.25 GiB, while the single-branch main clone fetched about 20k objects and 36 MiB.