WIP: reperform pass/delegate from current handler frame

[proboscis]

Summary

• change handle_forward() to read the current handler's ProgramDispatch from the current segment instead of recovering forwarding context via current_dispatch_id() / dispatch_origin_for_dispatch_id()
• reuse the current frame's effect, handler_continuation, and prompt marker when building the parent reperform path for Pass / Delegate
• drop the now-unused caller-visible helper that existed only to support the old DispatchId lookup path

Validation

• cargo check in packages/doeff-vm-core ✅
• uv run --with maturin maturin develop --release in packages/doeff-vm ✅
• uv run pytest tests/core/test_vm_ocaml5_violations.py -q ✅ 34 passed in 0.12s
• uv run pytest tests/test_pass_dispatch_context_regression.py -q ❌ timed out inside run(...)
• uv run pytest tests/test_cache_memo_rewriter_with_env.py -q ❌ timed out inside run(...)
• minimal manual repro (timeout 12s uv run python -u ...) printed only:
  • start run
  • program perform EffectA
    and then hung before any Python handler body executed

Current status

This is intentionally incomplete per issue guidance. The change moves Pass / Delegate toward an OCaml-5-style reperform that takes (effect, k) from the current handler frame instead of looking the dispatch context up by ID, but built-in handler layers are still reperforming into the wrong place before user handlers are reached.

Refs: vm-fix-dispatch-regression