Fix compatibility with Python >= 3.12

[avalentino]

The imp module was deprecated long time ago and it has been removed in Python 3.12

[bmcfee]

This change only affects doc builds; however, the doc builds have been failing for a bit due to changes in readthedocs.io. (missing .readthedocs.yaml) Would it be possible bring in a fix for that as well?

[codecov-commenter]

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Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 75.65%. Comparing base (a9d95eb) to head (d31c4c6). Report is 2 commits behind head on main.

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #122 +/- ## ========================================== + Coverage 74.78% 75.65% +0.86% ========================================== Files 4 4 Lines 115 115 ========================================== + Hits 86 87 +1 + Misses 29 28 -1 ``` | [Flag](https://app.codecov.io/gh/bmcfee/resampy/pull/122/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Brian+McFee) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/bmcfee/resampy/pull/122/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Brian+McFee) | `75.65% <ø> (+0.86%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Brian+McFee#carryforward-flags-in-the-pull-request-comment) to find out more.

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