SSA alpha route tests

The alpha SSA route is expected to run profile-owned optimization passes between AIR -> SSA lowering and SSA -> AIR emission.

The focused roundtrip tests protect two separate contracts:

• SsaRouteFactory.CreateRoundtripRoute(profile) must use the profile optimizer pipeline before emission.
• Raw new SsaRoundtripRoute(lowerer, emitter) remains a plain roundtrip path and does not run optimizers implicitly.

This distinction matters because the alpha arithmetic profile now owns the safe pass sequence:

1. SsaConstantFoldingPass
2. SsaBranchFoldingAndCleanupPass
3. SsaDeadPureInstructionEliminationPass

The route-level optimization test intentionally checks the emitted AIR shape for 2 3 add: after SSA optimization it should emit a single Push 5 after the entry label, not the original Push 2, Push 3, Intrinsic add sequence.