feat(codemode): support promise chaining

[rekram1-node]

Summary

• support eager sandbox promise chaining with then, catch, and finally
• return chainable promises from all, allSettled, and race
• flatten promises returned by handlers and preserve fulfillment/rejection pass-through semantics
• defer handlers past synchronous execution and reject self-resolving chains
• preserve native Promise.race loser behavior while draining work within the execution lifetime
• accept supported CodeMode callables as handlers and update runtime guidance

Tests

• bun test from packages/codemode (288 pass)
• bun typecheck from packages/codemode
• git diff --check