Release v3.19.20

Release v3.19.20 - Critical Bug Fix Release

STOP THE LINE Campaign Complete - 4 P0 BLOCKING bugs fixed

Highlights:
- ✅ 4 Critical Bugs Fixed: DEPYLER-0264, 0265, 0266, 0267
- 🔬 Investigation: DEPYLER-0268 verified as non-issue
- 🧪 21 New Regression Tests: Comprehensive test coverage
- 🎯 Zero Regressions: All existing tests pass

Bug Fixes:
- DEPYLER-0264: Fixed DynamicType undefined for untyped collections
- DEPYLER-0265: Fixed iterator dereferencing in for loops
- DEPYLER-0266: Fixed boolean conversion for collection empty checks
- DEPYLER-0267: Fixed .copied() vs .cloned() for non-Copy types
- DEPYLER-0268: Verified negative indexing works correctly (regression tests added)

Test Coverage:
- 3 tests for DEPYLER-0264 (untyped collections)
- 4 tests for DEPYLER-0265 (iterator dereferencing)
- 5 tests for DEPYLER-0266 (boolean conversion)
- 4 tests for DEPYLER-0267 (index access)
- 5 tests for DEPYLER-0268 (negative indexing regression)

All tests passing. Zero regressions.