Add more type annotations to expansion helpers #1846

Job	Run time
Tests for downstream project pytential	36m 9s
Ruff	10s
Conda Pytest Symengine with Loopy FFT	35m 29s
Conda Pytest	32m 51s
Documentation	2m 9s
basedpyright	2m 25s
Conda Examples	2m 18s
Conda Pytest Symengine	31m 59s
Typos	4s
	2h 23m 34s

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