Dipole broadcasting

[jcapriot]

Update the tdem and fdem dipoles to better support broadcasting, and use sympy analytics to test their implementations.

[codecov]

Codecov Report

Attention: Patch coverage is 98.69110% with 5 lines in your changes missing coverage. Please review.

Project coverage is 85.88%. Comparing base (d72b4c1) to head (87af1b7).
Report is 34 commits behind head on main.

Files with missing lines	Patch %	Lines
geoana/em/static/wholespace.py	97.93%	3 Missing ⚠️
geoana/em/base.py	81.81%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #76      +/-   ##
==========================================
- Coverage   87.46%   85.88%   -1.58%     
==========================================
  Files          30       31       +1     
  Lines        3079     3139      +60     
==========================================
+ Hits         2693     2696       +3     
- Misses        386      443      +57     

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