Clang ARC Lessons: AIMS Optimization Enhancements

Adopt battle-tested ARC optimization patterns from Clang/LLVM and Swift into Ori's AIMS pipeline: effect-aware coalescing barriers, compile-time statistics, physical-refcount-based nested pair elimination, late COW compound contraction, and PRE-style global RC code motion. AIMS is architecturally stronger than Clang's per-pointer state machine — these enhancements add the "outer ring" of legality/profitability machinery around the existing semantic core.