Test Suite Health: LCFail Elimination & Performance Optimization

Restore the Ori test suite to full health across two fronts: (1) audit, categorize, and reprioritize the LLVM backend roadmap (Section 21A) so that LCFail tests can be driven from 3,956 to 0 via an impact-ordered implementation sequence — this plan creates the tracking infrastructure and priority ordering, then the actual codegen implementation is executed via Section 21A's subsections in the new priority order, and (2) target reducing the cargo t wall time from ~59s to <=30s (-50%) by profiling the compiler, optimizing the AOT test pipeline, and eliminating hot-path inefficiencies — without modifying a single test. The 30s target is aspirational; profiling data may reveal a different achievable floor, in which case the target is revised with rationale.