feat(pulse-core): add filter predicate to EventEngine.subscribe()

[Jayking40]

# feat(pulse-core): EventEngine.subscribe() filter predicate

## Summary

Consumers that need only a subset of events (e.g. payments above a
threshold, only USDC transfers) previously had to receive every event
and discard unwanted ones in their own code. This change moves that gate
inside the engine so events that will never be consumed are suppressed
before they are emitted.

An optional [filter](cci:1://file:///home/jayking/projects/orbital_stellar/packages/pulse-core/test/pulse-core.test.ts:473:8-473:65) predicate can now be passed at subscribe time:

```ts
const watcher = engine.subscribe("GABC...", {
  filter: (event) =>
    event.type === "payment.received" && Number(event.amount) >= 100,
});

Only events for which filter returns true are delivered to that
watcher. All watchers without a filter behave exactly as before.

Changes

• New SubscribeOptions type exported from the package — carries the
  optional filter predicate so callers get full TypeScript support.
• subscribe(address, options?) — extended signature stores the
  predicate in a per-address filters map; the existing stop handler
  now also removes the entry from that map when the watcher is stopped.
• passesFilter(address, event) — private helper that invokes the
  predicate inside a try/catch. A throwing predicate is treated as a
  rejection and a [pulse-core] warning is logged; the engine keeps
  running.
• route() — calls passesFilter() once per watcher before
  emitting both the specific event type and the * wildcard. The
  payment-type resolution was also deduplicated as a minor side-effect.
• Three new unit tests covering all three required scenarios:
  filter accepts, filter rejects, and filter throws (engine survives).

Testing

The full @orbital/pulse-core test suite was run with:

pnpm --filter @orbital/pulse-core test

Result: 17 tests pass, 0 failures.

New tests added under describe("subscribe() filter predicate"):

Test	Scenario
delivers events to a watcher whose filter returns true	Happy path — matching event reaches the handler
suppresses events for a watcher whose filter returns false	Reject path — no handler fires, neither on specific type nor *
treats a throwing filter as a reject and logs a warning	Safety path — handler suppressed, warning logged, engine routes subsequent events normally

Closes #83

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