Add new functions to get Earth boresight angles and Earth block intervals

[taldcroft]

Description

This provides a new function to get the angle from the Chandra ACA boresight to the Earth limb and Earth center over a date range. It also provides the Earth opening angle at the same time sampling.

It also adds a simple convenience function to get time intervals when the boresight to limb angle is below a certain value (10 deg by default).

Interface impacts

Adds two new functions. This PR is a requirement for sot/kalman_watch#11.

Testing

Unit tests

• Mac

(masters) ➜  chandra_aca git:(boresight-angle) $ git rev-parse HEAD 
f1a501c8417528d3a10b3edfe24e972b08a225b3
(masters) ➜  chandra_aca git:(boresight-angle) $ pytest
======================================================== test session starts ========================================================
platform darwin -- Python 3.10.8, pytest-7.2.1, pluggy-1.0.0
rootdir: /Users/aldcroft/git, configfile: pytest.ini
plugins: timeout-2.1.0, anyio-3.6.2
collected 202 items                                                                                                                 

chandra_aca/tests/test_aca_image.py ..............                                                                            [  6%]
chandra_aca/tests/test_all.py ........................                                                                        [ 18%]
chandra_aca/tests/test_attitude.py .............................................................                              [ 49%]
chandra_aca/tests/test_dark_model.py ....                                                                                     [ 50%]
chandra_aca/tests/test_drift.py ..........................                                                                    [ 63%]
chandra_aca/tests/test_maude_decom.py ..................                                                                      [ 72%]
chandra_aca/tests/test_planets.py ...............                                                                             [ 80%]
chandra_aca/tests/test_psf.py ...                                                                                             [ 81%]
chandra_aca/tests/test_residuals.py ss...                                                                                     [ 84%]
chandra_aca/tests/test_star_probs.py ................................                                                         [100%]

================================================== 200 passed, 2 skipped in 44.01s ==================================================

Independent check of unit tests by [REVIEWER NAME]

• [PLATFORM]:

Functional tests

From this PR

From MATLAB MCC

[javierggt]

I ran the tests and went over the code and it looks reasonable to me. The things I pointed out are trivial, basically improving a docstring and adding one small test.

The third comment (moving np.sawpaxes into the call to np.einsum) is your call.

[taldcroft]

@javierggt - I addressed your comments in f1a501c. And I noticed a comment mistake which is fixed in 733d4e6.