PERF: Optimize month_position_check in infer_freq

[jbrockmendel]

Claude wrote this, I reviewed it manually

dti = pd.date_range("2000-01-31", periods=10000, freq="ME")._with_freq(None)

%timeit pd.infer_freq(dti)
5.15 ms ± 692 μs per loop (mean ± std. dev. of 7 runs, 100 loops each)  # <- main
686 μs ± 91.4 μs per loop (mean ± std. dev. of 7 runs, 1,000 loops each)  # <- PR

Summary

• Replace Python-level zip() iteration with C-level indexed range() loop in month_position_check
• Type the weekdays parameter as an int32_t[:] memoryview instead of untyped Python object
• Add @cython.boundscheck(False) and @cython.wraparound(False) decorators

[mroeschke]

Thanks @jbrockmendel