Don't crash Python interpreter via assert(false) when missing cublaslt

[akx]

As discussed in #984 (comment).

Before:

tests/test_functional.py::test_dequant_mm[dim1_121_dim4_201_dims_2_formatB_col_turing_has_bias_True] Fatal Python error: Aborted

Thread 0x00007fdb0d0e7640 (most recent call first):
  <no Python frame>

Current thread 0x00007fdc47e18000 (most recent call first):
  File "/home/akx/bitsandbytes/bitsandbytes/functional.py", line 1930 in igemmlt
  File "/home/akx/bitsandbytes/tests/test_functional.py", line 990 in test_dequant_mm
  [...]

Aborted

After:

tests/test_functional.py::test_dequant_mm[dim1_121_dim4_201_dims_2_formatB_col_turing_has_bias_True] FAILED
[...]
        if has_error == 100:  # `ERR_NOT_IMPLEMENTED` is defined as 100 in `ops.cu`
>           raise NotImplementedError("igemmlt not available (probably built with NO_CUBLASLT)")
E           NotImplementedError: igemmlt not available (probably built with NO_CUBLASLT)

[Titus-von-Koeller]

Amazing, you're finding, raising, fixing issues at lightning speed. Some sort of Jedi master thing :D

Thanks so much.

Anyways, the test suite is a major piece of work. The author and main contributor only ran the test suite very selectively for whatever he was currently working on, judging by eye and experience if the results were meaningful or not.

We just took over maintenance fully since December and are still finding our way around the code in many things.

Let's talk about this some more.

[Titus-von-Koeller]

Are you on Slack? If you want, I would like to include you in the HF bnb-daily-ci channel (even if bnb test suite itself is not run there yet) and the bitsandbytes collab channel.

[akx]

Amazing, you're finding, raising, fixing issues at lightning speed.

Thanks 😅

Are you on Slack? If you want, I would like to include you in the HF bnb-daily-ci channel (even if bnb test suite itself is not run there yet) and the bitsandbytes collab channel.

I am, though I can't guarantee I can be super active (day job at @valohai, other life stuff, all that). If you need an email address, use the one in my commits or on my profile.