fix(transform): #1047 — async early return followed by an unreached await

[proggeramlug]

Summary

Fixes #1047. The generator transform only rewrote user-level return X statements when the state's exit was StateExit::Done. States ending in StateExit::Yield (i.e. states followed by an await) left those returns as raw Stmt::Return(X), so when an early return was taken next() returned the bare expression value; the AsyncStepChain caller treated the missing .done as false and re-entered the same state — infinite loop.

The fix runs the same body_contains_return → prepend_done_before_returns + rewrite_returns_as_done sequence on Yield-state bodies that StateExit::Done already does.

Reproducer

async function getKid(): Promise<string> {
    const existing = await findExisting();      // state 0 → 1 (Yield)
    if (existing) return existing.kid;           // <-- raw Return inside state 1
    const kid = `dek-${Date.now().toString(36)}`;
    await insertNew(kid);                        // state 1 → 2 (Yield, unreached)
    return kid;
}

Before: infinite loop, [inner] existing: the-kid printed millions of times.
After: k: the-kid typeof: string — matches Node byte-for-byte.

Test plan

• test-files/test_issue_1047_async_early_return_unreached_await.ts matches node --experimental-strip-types
• Focused build green
• No regressions in existing async tests (cargo build --release -p perry-transform -p perry)