feat(timers): implement node:timers/promises setTimeout/setImmediate (#1213)

[proggeramlug]

Summary

node:timers/promises setTimeout(delay, value?) and setImmediate(value?) were unimplemented stubs that threw '… is not yet implemented', so await setTimeout(ms) / await setTimeout(ms, value) never resolved (part of the #1213 node:timers parity tracker / #793).

Both are now wired to the existing promise-returning timer primitive js_set_timeout_value, returning a Promise that resolves with value (or undefined). setTimeout is registered with arity 2 so the closure dispatch pads a missing value arg with undefined; setImmediate resolves on a later turn (0-delay). No closure synthesis needed — composes the existing tested timer→promise plumbing.

Test

• Flips test_parity_timers_promises to PASS (removed from known_failures.json).
• Flips node-suite/timers/promises/shadowed-global-fast-paths to PASS — removed the stale test-parity/expected/ snapshot that recorded the old stub error, so it now compares against live Node (both produce setTimeout resolved object {"a":1} / setImmediate resolved object {"b":2}).
• Verified value + no-value forms match Node:

await setTimeout(10)        // resolves undefined
await setTimeout(10, 'VAL') // resolves 'VAL'
await setImmediate('iv')    // resolves 'iv'

Remaining #1213 sub-gaps (separate follow-ups): setInterval async-iterator, scheduler/AbortSignal paths, numeric timer clears, and timer-callback this binding.

Refs #1213.