Convert CBMAEstimator method to function

[tsalo]

Closes None. This is mostly an effort to minimize the diff and clean up the changelog for #655.

Changes proposed in this pull request:

• Standardize example header lengths.
• Replace manual connectivity matrix definition with calls to scipy.ndimage.generate_binary_structure.
• Convert CBMAEstimator._calculate_cluster_measures to a function.
• Some miscellaneous docstring and spacing cleanup.
• Document and test the vfwe_only fix from Reorganize and streamline examples #656.

[codecov]

Codecov Report

Merging #658 (d091eb5) into main (bdc0363) will increase coverage by 0.04%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #658      +/-   ##
==========================================
+ Coverage   85.29%   85.33%   +0.04%     
==========================================
  Files          40       40              
  Lines        4542     4529      -13     
==========================================
- Hits         3874     3865       -9     
+ Misses        668      664       -4     

Impacted Files	Coverage Δ
nimare/diagnostics.py	93.61% <100.00%> (-0.27%)	⬇️
nimare/meta/cbma/base.py	96.53% <100.00%> (+1.22%)	⬆️
nimare/meta/cbma/mkda.py	97.04% <100.00%> (-0.05%)	⬇️
nimare/meta/utils.py	52.80% <100.00%> (+5.68%)	⬆️

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