* fix(hwfit): tolerate non-numeric gpu_count in /api/hwfit/models
The route did `n = int(gpu_count)` with no guard, so a non-numeric query param
like `?gpu_count=abc` raised ValueError and returned HTTP 500. Parse it
defensively (mirroring the gpu_group guard a few lines above): a malformed value
is ignored, exactly like omitting the param, and valid values still apply.
Adds tests/test_hwfit_gpu_count_nonnumeric.py: a non-numeric gpu_count returns a
ranking instead of raising, and a numeric value is still accepted.
* test(hwfit): cover non-numeric manual_gpu_count too
Follow-up to the gpu_count guard: add a regression test for the sibling
manual_gpu_count query param (the hardware simulator in _apply_manual_hardware),
which dev already guards by defaulting to 1 on a non-numeric value. This pins
that behaviour so the endpoint's count parsing is fully covered and cannot
regress to a 500.
