Add LETID tests and geospatial bug fixes

[martin-springer]

Describe your changes

• Add basic tests to LETID module
• Bug fixes for geospatial analysis

Type of change

• [x] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)

Checklist before requesting a review

• [x] I have performed a self-review of my code
• [x] Code changes are covered by tests.
• [x] Code changes have been evaluated for compatibility/integration with Scenario analysis (for future PRs)
• [x] New functions added to init.py
• [x] API.rst is up to date, along with other sphinx docs pages
• [x] Example notebooks are rerun and differences in results scrutinized
• [x] What's new changelog has been updated in the docs

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 57.48031% with 162 lines in your changes are missing coverage. Please review.

Project coverage is 63.40%. Comparing base (afe636e) to head (a4ffcb8). Report is 1 commits behind head on main.

Files	Patch %	Lines
pvdeg/weather.py	20.21%	75 Missing :warning:
pvdeg/standards.py	11.76%	30 Missing :warning:
pvdeg/geospatial.py	6.45%	29 Missing :warning:
pvdeg/utilities.py	20.68%	23 Missing :warning:
pvdeg/degradation.py	0.00%	3 Missing :warning:
pvdeg/humidity.py	50.00%	1 Missing :warning:
pvdeg/spectral.py	91.66%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #77 +/- ## =========================================== + Coverage 47.72% 63.40% +15.68% =========================================== Files 28 29 +1 Lines 1800 2077 +277 =========================================== + Hits 859 1317 +458 + Misses 941 760 -181 ```

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