Ensure `angular_dist` returns a valid values

[ortk95]

For some input values (e.g. for identical input points), SpiceBase.angular_dist returned NaN. This was due to the accumulation of small floating point errors causing the code to evaluate e.g. np.arccos(1.0000000000000002) -> NaN rather than the correct np.arccos(1.0) -> 0.0. This has been fixed by clipping the value in np.arccos to ensure it always lies between -1 and 1.

Closes #357

Pull request checklist

• [x] Add a clear description of the change
• [x] Add any new tests needed
• [x] Run spell check on new text visible to user (documentation, GUI etc.)
• [x] Check any changes to requirements.txt are reflected in setup.py and conda-forge feedstock
• [x] Check code passes CI checks (run run_ci.sh or check GitHub Actions)

See CONTRIBUTING.md for more details.

[coveralls]

Pull Request Test Coverage Report for Build 9480837579

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Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 99.561%

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Totals
Change from base Build 9480466937:	0.0%
Covered Lines:	2955
Relevant Lines:	2968

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💛 - Coveralls