Make connectivity field names compatible with MATLAB

[tsalo]

Closes #164.

Changes proposed in this pull request

• Add "atlas_" prefix to field names in connectivity MAT files. This will ensure that no fields start with a number (e.g., an atlas name that starts with a number, like 4S*), which is an issue for MATLAB.
• Replace dashes with underscores in measure names. This should change small-worldness to small_worldness.

Documentation to review

• https://qsirecon--166.org.readthedocs.build/en/166/connectivity_matrices.html

[tsalo]

We should probably document the connectivity files based on @valeriejill's pre-split QSIPrep PR: PennLINC/qsiprep#689

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 5 lines in your changes missing coverage. Please review.

Project coverage is 33.94%. Comparing base (64be9d6) to head (e5b3420).

Files with missing lines	Patch %	Lines
qsirecon/interfaces/dsi_studio.py	0.00%	4 Missing ⚠️
qsirecon/interfaces/mrtrix.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #166      +/-   ##
==========================================
- Coverage   33.94%   33.94%   -0.01%     
==========================================
  Files          57       57              
  Lines        7193     7195       +2     
  Branches      983      983              
==========================================
  Hits         2442     2442              
- Misses       4653     4655       +2     
  Partials       98       98              

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

---

🚨 Try these New Features:

• Flaky Tests Detection - Detect and resolve failed and flaky tests