Fix age calculation to match R pipeline behavior

Add automatic age correction from date of birth (DOB) to match R pipeline's
fix_age() function. This ensures data quality by always calculating age from
DOB rather than trusting potentially incorrect Excel values.

Changes:
- Add _fix_age_from_dob() function in clean/patient.py (step 5.5)
- Calculate age: tracker_year - birth_year - (1 if tracker_month < birth_month else 0)
- Log warnings and track errors via ErrorCollector for all age corrections
- Handle missing ages, mismatched ages, and negative ages (set to error value)

Validation:
- Tested with 2025_06_CDA tracker: 35 age errors properly corrected and tracked
- Results now match R output (e.g., patient KH_CD016: 18 years, not 21)
- Improvement over R: structured error tracking instead of logging only

Also adds:
- compare_r_vs_python.py: Comprehensive comparison tool for validation
- fastexcel dependency: Required for Excel reading in comparison scripts

Fixes critical data quality issue where incorrect ages from Excel were
propagated to final datasets. Now matches R pipeline behavior while
providing better error tracking and documentation.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: pmayd

a4d-python/pyproject.toml

@@ -24,6 +24,7 @@ dependencies = [
     "rich>=13.7.0",
     "tqdm>=4.66.0",
     "python-dateutil>=2.8.0",
+    "fastexcel>=0.16.0",
 ]