fix: attention bug with large values

[gaetansnl]

reproduced pytorch nightly
needs in depth tests

[pommedeterresautee]

lgtm
Seems to me we can simplify code, but need to do some checks.
Priority to security and precision, let's merge!

[pommedeterresautee]

I am bit surprised that we can't remove (and related lines):

            if NEED_LOAD_MASK_SIZE_N:
                attention_load_mask = (n_row_offset + offs_n)[None, :] < size_n

as it seems redundant with the newly added check (made many tests, crash precision). Triton is mysterious sometimes.