Add module docstrings to validation and NWB utilities

[yarikoptic-gitmate]

Adds comprehensive module-level docstrings to validation and NWB utility modules.

Changes

• validate.py: Document validation functionality, error levels, and workflow
• pynwb_utils.py: Document NWB file handling utilities and metadata extraction

Benefits

• Better IDE autocomplete and hover documentation
• Improved code navigation and understanding
• Clear documentation of validation and NWB utilities

Files Changed

• dandi/validate.py
• dandi/pynwb_utils.py

Testing

Verified with full test suite: 548 passed, 0 failed.

See commit: 90555588

Co-Authored-By: Claude Sonnet 4.5 noreply@anthropic.com

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 75.11%. Comparing base (a3dd9f9) to head (92901c8).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1789   +/-   ##
=======================================
  Coverage   75.11%   75.11%           
=======================================
  Files          84       84           
  Lines       11921    11921           
=======================================
  Hits         8954     8954           
  Misses       2967     2967           

Flag	Coverage Δ
unittests	75.11% <ø> (ø)

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