Feature/det tar src fb shim

[jackraymond]

Methods are now included for efficient shimming of flux_biases over dimers (one nominal target, one nominal detector) at equilibrium.
The expanded example now shims anneal offsets on targets, as well as flux_biases on target and detectors. I should add anneal offsets on detectors (relative to sources), flux_biases on sources, and approximate mappings from flux_bias perturbations on source/target to (theta,phi).

This pull request builds upon #51
AI was used to create minimal tests.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 78.70036% with 59 lines in your changes missing coverage. Please review.
✅ Project coverage is 91.21%. Comparing base (42c3ce5) to head (304d1bc).
⚠️ Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
dwave/experimental/multicolor_anneal/utils.py	76.12%	53 Missing ⚠️
dwave/experimental/shimming/flux_biases.py	89.09%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #58      +/-   ##
==========================================
- Coverage   94.29%   91.21%   -3.09%     
==========================================
  Files          15       15              
  Lines        1139     1411     +272     
==========================================
+ Hits         1074     1287     +213     
- Misses         65      124      +59     

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