Add support for Python 3.11

[desilinguist]

• Replace deprecated inspect.getargspec() in rescaled decorator.
• Switch Azure Pipeline to Python 3.11.
• Add Python 3.11 to README.rst, setup.py, and CONTRIBUTING.md.

Closes #744.

[codecov[bot]]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (d47ba10) 95.24% compared to head (f900b49) 95.24%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #749 +/- ## ======================================= Coverage 95.24% 95.24% ======================================= Files 29 29 Lines 3578 3578 ======================================= Hits 3408 3408 Misses 170 170 ``` | [Impacted Files](https://app.codecov.io/gh/EducationalTestingService/skll/pull/749?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=EducationalTestingService) | Coverage Δ | | |---|---|---| | [skll/learner/utils.py](https://app.codecov.io/gh/EducationalTestingService/skll/pull/749?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=EducationalTestingService#diff-c2tsbC9sZWFybmVyL3V0aWxzLnB5) | `93.37% <100.00%> (ø)` | |

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