feat: Add test for solid harmonic moment translation (#159)

[tutou2356]

Adds a unit test (test_multipole_translation) to verify that solid harmonic moments calculated by Grid.moments behave correctly under origin translation, as required by issue #159. The test compares numerical results against the analytical formula and passe.

[Copilot]

Copilot reviewed 1 out of 1 changed files in this pull request and generated no comments.

Comments suppressed due to low confidence (1)

src/grid/tests/test_molgrid.py:78

• [nitpick] Consider renaming the variable 'l_check' (used for recalculating 'l' in get_lm_from_horton_index) to a more descriptive name, such as 'corrected_l', to improve code clarity.

l_check = 0

[tutou2356]

Hi! @PaulWAyers @marco-2023 @Ali-Tehrani I’ve addressed the feedback from Copilot AI by renaming l_check to corrected_l for better clarity. The updated code has been pushed, and all tests still pass. Please let me know if there’s anything else to address! Thanks!