[Packaging] Shrink wheel ~35 % via nvcc --compress-mode=size

[trmanish]

What this PR does

• Appends --compress-mode=size to CMAKE_CUDA_FLAGS for nvcc ≥ 12.4.
• No runtime or API changes.

Impact

• Wheel shrinks 69 MB → 45 MB (≈ 35 %).

Compatibility

• nvcc < 12.4 builds unchanged—the flag is gated by a version check.
• Decompression adds only a few hundred ms on first import bitsandbytes.

[matthewdouglas]

Thanks, appreciate the suggestion! I have the same concern mentioned over on PyTorch regarding support for users with older drivers: pytorch/pytorch#157791 (comment)

Mainly it seems that this would require cu124+ users to have the 550+ driver, while currently we should still have compatibility for driver version 525+.

So will have to weigh that in as a consideration.

[trmanish]

I believe an earlier comment from original PR did say it won't have that as a requirement

pytorch/pytorch#157791 (comment)

But I believe latest from Pytorch is as below:

pytorch/pytorch#157791 (comment)

However my understanding is(pls correct me if wrong) that the only variant that would be built with --compress-mode=size is the cu124 wheel, and that wheel already implies a 550-series driver. Users on 525/535 stay on the cu122 / cu121 wheels, which this PR leaves untouched.

Options
Merge as-is – compression only affects the cu124 wheel, no compatibility regression for existing users.

Opt-in flag – guard it behind ENABLE_BNB_CUDA_COMPRESSION=1; default off.

Dual wheels – publish both bitsandbytes-cu124.whl and -cu124-slim.whl.