fix: move Argon2id KDF off the main thread in payments send() [AMB-3036]

[bufo24]

Context

This is the upstream fix for the temporary @ambosstech/payments@1.1.0 pnpm patch in amboss-internal-api#551. Once this SDK release is available, internal-api can remove that patch.

Problem

Live-wallet sends derive credentials with two memory-hard Argon2id passes. The previous synchronous implementation ran both passes on Node’s main thread, blocking timers, socket I/O, and health probes for several seconds. This caused the internal API to lose its RabbitMQ connection while processing payments.

Fix

• Move Argon2id work to a lazily created, shared node:worker_threads worker.
• Keep the cryptographic inputs, parameters, and outputs byte-for-byte compatible.
• Keep the worker referenced briefly between chained jobs, then unref it while idle so short-lived processes can exit normally.
• Update the callers for the asynchronous KDF API and keep send preparation sequential to avoid unnecessary memory pressure.
• Document that preparation no longer blocks the event loop, while still avoiding first-payment KDF latency.

The worker is deliberately single-threaded: the second KDF depends on the first output, and a pool would add lifecycle complexity without helping that dependency.

Validation

• pnpm test
• pnpm typecheck
• pnpm --filter @ambosstech/payments run test:examples
• pnpm --filter @ambosstech/payments run typecheck:examples

The new Argon2 tests lock the known derivation outputs and assert that a timer remains responsive while hashing.