feat: callback-driving adapter for P3 async fusion

[avrabe]

Summary

Implements P3 async cross-component call fusion using a callback-driving adapter that runs entirely in core wasm — no canon lift/canon lower inside the fused component, no call_might_be_recursive trap.

The adapter drives the callee's [async-lift] + [callback] loop directly:

1. Call [async-lift] entry → packed i32 (EXIT/WAIT/YIELD)
2. Loop: if WAIT, call waitable-set-poll; call [callback] with event
3. After EXIT, read result from task.return shim globals

Key changes

• Callback-driving adapter (fact.rs): generates core wasm function that drives the async callback protocol
• Task.return shims (lib.rs): in-module functions that store result values to globals, replacing canonical task.return
• Per-site shim matching: maps each async function to its specific shim by original function name
• Retptr support: handles the return-pointer convention for multi-value results
• Cross-memory string copy: copies string results from callee to caller memory via cabi_realloc + memory.copy
• Cleanup: removed dead AsyncLiftLower code path from component_wrap.rs
• Handle tables (issue 3-component re-exporter resource chains: implement shim module approach #92): infrastructure for re-exporter resource chains (WIP)

Runtime results on stock wasmtime 41

prime 7      → 7 is prime           ✅
fibonacci 10 → fibonacci(10) = 55   ✅
factorial 5  → factorial(5) = 120   ✅
collatz 27   → collatz(27) = 111    ✅
analyze      → needs param copy     ❌ (string params not yet copied)

No wasmtime fork. No special flags beyond -W component-model-async=y.

Remaining

• String/list PARAM cross-memory copy (text functions need input params copied from caller→callee memory)
• Complex result types (records with nested pointers)
• Issue 3-component re-exporter resource chains: implement shim module approach #92: re-exporter handle table null pointer issue

Test plan

• 73/73 P2 runtime tests pass
• P3 core module validates
• P3 component validates with --features cm-async
• P3 compute functions correct on stock wasmtime
• P3 text functions (blocked on param cross-memory copy)

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