TYP: enable disallow-untyped-decorators in CI
xref https://github.com/pandas-dev/pandas/pull/33160#issuecomment-608707397

in order to ensure adding decorators or changing existing decorators don't lose types on our typed functions, we could enable this flag, after resolving the current violations. (expand details)

<details>

$ mypy pandas --disallow-untyped-decorators
pandas\core\window\numba_.py:58: error: Untyped decorator makes function "roll_apply" untyped
pandas\tseries\offsets.py:458: error: Untyped decorator makes function "freqstr" untyped
pandas\core\nanops.py:97: error: Untyped decorator makes function "f" untyped
pandas\core\nanops.py:477: error: Untyped decorator makes function "nansum" untyped
pandas\core\nanops.py:799: error: Untyped decorator makes function "nansem" untyped
pandas\core\nanops.py:849: error: Untyped decorator makes function "reduction" untyped
pandas\core\nanops.py:880: error: Untyped decorator makes function "nanargmax" untyped
pandas\core\nanops.py:916: error: Untyped decorator makes function "nanargmin" untyped
pandas\core\nanops.py:952: error: Untyped decorator makes function "nanskew" untyped
pandas\core\nanops.py:1036: error: Untyped decorator makes function "nankurt" untyped
pandas\core\nanops.py:1129: error: Untyped decorator makes function "nanprod" untyped
pandas\core\nanops.py:1309: error: Untyped decorator makes function "nancorr" untyped
pandas\core\nanops.py:1364: error: Untyped decorator makes function "nancov" untyped
pandas\core\apply.py:136: error: Untyped decorator makes function "dtypes" untyped
pandas\tseries\frequencies.py:333: error: Untyped decorator makes function "is_unique" untyped
pandas\tseries\frequencies.py:337: error: Untyped decorator makes function "is_unique_asi8" untyped
pandas\core\arrays\period.py:270: error: Untyped decorator makes function "dtype" untyped
pandas\core\base.py:198: error: Untyped decorator makes function "ndim" untyped
pandas\core\indexes\base.py:1619: error: Untyped decorator makes function "is_unique" untyped
pandas\core\indexes\base.py:1973: error: Untyped decorator makes function "inferred_type" untyped
pandas\core\indexes\base.py:1980: error: Untyped decorator makes function "is_all_dates" untyped
pandas\core\indexes\base.py:2021: error: Untyped decorator makes function "hasnans" untyped
pandas\core\indexes\base.py:3840: error: Untyped decorator makes function "array" untyped
pandas\core\arrays\integer.py:62: error: Untyped decorator makes function "is_signed_integer" untyped
pandas\core\arrays\integer.py:66: error: Untyped decorator makes function "is_unsigned_integer" untyped
pandas\core\arrays\integer.py:74: error: Untyped decorator makes function "numpy_dtype" untyped
pandas\core\arrays\integer.py:79: error: Untyped decorator makes function "kind" untyped
pandas\core\arrays\integer.py:83: error: Untyped decorator makes function "itemsize" untyped
pandas\core\arrays\integer.py:341: error: Untyped decorator makes function "dtype" untyped
pandas\core\arrays\categorical.py:497: error: Untyped decorator makes function "size" untyped
pandas\core\arrays\categorical.py:504: error: Untyped decorator makes function "itemsize" untyped
pandas\core\indexes\numeric.py:452: error: Untyped decorator makes function "is_unique" untyped
pandas\core\indexes\range.py:170: error: Untyped decorator makes function "_int64index" untyped
pandas\core\indexes\range.py:280: error: Untyped decorator makes function "nbytes" untyped
pandas\core\indexes\range.py:325: error: Untyped decorator makes function "is_monotonic_increasing" untyped
pandas\core\indexes\range.py:329: error: Untyped decorator makes function "is_monotonic_decreasing" untyped
pandas\core\indexes\multi.py:1133: error: Untyped decorator makes function "dtype" untyped
pandas\core\indexes\multi.py:1152: error: Untyped decorator makes function "nbytes" untyped
pandas\core\indexes\multi.py:1414: error: Untyped decorator makes function "inferred_type" untyped
pandas\core\indexes\multi.py:1450: error: Untyped decorator makes function "is_monotonic_increasing" untyped
pandas\core\indexes\multi.py:1474: error: Untyped decorator makes function "is_monotonic_decreasing" untyped
pandas\core\indexes\datetimes.py:279: error: Untyped decorator makes function "_is_dates_only" untyped
pandas\core\indexes\period.py:348: error: Untyped decorator makes function "_int64index" untyped
pandas\core\indexes\interval.py:384: error: Untyped decorator makes function "_multiindex" untyped
pandas\core\indexes\interval.py:388: error: Untyped decorator makes function "values" untyped
pandas\core\indexes\interval.py:430: error: Untyped decorator makes function "is_monotonic_decreasing" untyped
pandas\core\indexes\interval.py:1031: error: Untyped decorator makes function "intersection" untyped
pandas\core\groupby\ops.py:257: error: Untyped decorator makes function "is_monotonic" untyped
pandas\core\groupby\ops.py:270: error: Untyped decorator makes function "codes_info" untyped
pandas\core\groupby\ops.py:288: error: Untyped decorator makes function "ngroups" untyped
pandas\core\groupby\ops.py:298: error: Untyped decorator makes function "result_index" untyped
pandas\core\groupby\ops.py:818: error: Untyped decorator makes function "reconstructed_codes" untyped
pandas\core\groupby\grouper.py:395: error: Untyped decorator makes function "result_index" untyped
pandas\core\groupby\grouper.py:420: error: Untyped decorator makes function "groups" untyped
pandas\core\window\rolling.py:1802: error: Untyped decorator makes function "is_datetimelike" untyped
pandas\core\window\rolling.py:1808: error: Untyped decorator makes function "_on" untyped
pandas\tests\frame\methods\test_replace.py:14: error: Untyped decorator makes function "mix_ab" untyped
pandas\tests\frame\methods\test_replace.py:19: error: Untyped decorator makes function "mix_abc" untyped
Found 58 errors in 20 files (checked 987 source files)

</details>
