Add Phase 122+ modernization recommendations

Comprehensive analysis of next modernization opportunities:

Tier 1 (High-Value, Low-Risk):
- Phase 122: constexpr expansion (50+ getters, 2-3 hours)
- Phase 123: [[nodiscard]] annotations (30-40 functions, 4-6 hours)
- Phase 124: Constant macros to constexpr (15-20 macros, 2-3 hours)

Tier 2 (Medium-Value, Medium-Risk):
- Phase 125: GC macro modernization (5-7 macros, requires benchmarking)
- Phase 126: std::span expansion (20-30 sites, requires careful benchmarking)

Tier 3 (Defer):
- Range-based for loops (limited benefit)
- Loop counter/size conversions (high risk, low value)
- cast() macro elimination (massive scope)

Status update:
- Boolean conversions: Already complete! (5/8 already done, 3/8 not boolean functions)
- Constructor patterns: Already using member initializer lists (Phase 122)
- Current performance: 4.26s avg (better than 4.33s target)

Includes specific file locations, line numbers, code examples, and detailed
risk assessments for each opportunity.

Author: claude