Enhancement of the `UVWindow` module

[adeliegorce]

This PR inludes several small changes to the UVWindow module, which should all be backward-compatible. Namely:

• Applied nan_to_num function to weights in grouping.spherical_average to ensure there are no NaN weights (the real parts are never NaN but the imaginary part is sometimes)
• The way to feed a beam model to the UVWindow.from_uvpspec method is now through the ftbeam key (previously ftfile). It can the path to a beam simulation (Path or str) or a FTBeam object directly. This facilitates using Gaussian beam models.
• Added related tests.

[adeliegorce]

NB: This update is required for the PR #49 "Cylindrical window functions implementation" of pspec_likelihood (see https://github.com/HERA-Team/pspec_likelihood/pull/49) to be merged (checks fail without).

[codecov[bot]]

Codecov Report

Base: 95.92% // Head: 95.92% // Increases project coverage by +0.00% :tada:

Coverage data is based on head (5c394f9) compared to base (0122345). Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #368 +/- ## ======================================= Coverage 95.92% 95.92% ======================================= Files 17 17 Lines 6038 6043 +5 ======================================= + Hits 5792 5797 +5 Misses 246 246 ``` | Flag | Coverage Δ | | |---|---|---| | unittests | `95.92% <100.00%> (+<0.01%)` | :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=HERA-Team#carryforward-flags-in-the-pull-request-comment) to find out more. | [Impacted Files](https://codecov.io/gh/HERA-Team/hera_pspec/pull/368?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=HERA-Team) | Coverage Δ | | |---|---|---| | [hera\_pspec/grouping.py](https://codecov.io/gh/HERA-Team/hera_pspec/pull/368/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=HERA-Team#diff-aGVyYV9wc3BlYy9ncm91cGluZy5weQ==) | `97.53% <100.00%> (+<0.01%)` | :arrow_up: | | [hera\_pspec/pspecdata.py](https://codecov.io/gh/HERA-Team/hera_pspec/pull/368/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=HERA-Team#diff-aGVyYV9wc3BlYy9wc3BlY2RhdGEucHk=) | `97.03% <100.00%> (ø)` | | | [hera\_pspec/uvpspec.py](https://codecov.io/gh/HERA-Team/hera_pspec/pull/368/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=HERA-Team#diff-aGVyYV9wc3BlYy91dnBzcGVjLnB5) | `97.54% <100.00%> (ø)` | | | [hera\_pspec/uvwindow.py](https://codecov.io/gh/HERA-Team/hera_pspec/pull/368/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=HERA-Team#diff-aGVyYV9wc3BlYy91dndpbmRvdy5weQ==) | `98.16% <100.00%> (+0.01%)` | :arrow_up: | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=HERA-Team). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=HERA-Team)

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