JIT quantized-kernel fixes; adjacent minor underscore fix

[dwijenpatel]

Small PR fixing #4350

• the added results_per_simdgroup param is unused, but needed to fix the compilation issue, and the underlying implementations hardcode 4.
• fp_qmv_fast was mentioned in the issue, but has the correct param count (and actually uses results_per_simdgroup). The other 3 mentioned are fixed in this PR.
• Running the full test_quantized suite under JIT surfaced two pre-existing, unrelated errors - removing underscores in two get_qmm_nax_kernel_wrapped calls to reference correct function names, re-ran tests to verify all fixes (37/37, AOT unchanged).
• Adding a MLX_METAL_JIT=ON job to CI might be worth doing at some point, to proactively surface this class of bugs.

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• ☑️ I understand it is strictly prohibited to use AI to write PR description
• AI usage disclosure:
  Pair-programming with Claude, attempting to do useful work as a side-effect of deep-diving into GPU kernel optimization.