feat(message-bus)!: rewrite around class-based events and per-broker queues

[johngeorgewright]

Replace the MessageBus API (string event names, tuple args, generators and
RPC-style invokables) with a class-based bus. Events are plain class instances
routed by constructor identity, so EventDescriptions are no longer needed. The
invokable and generator APIs collapse into a single streaming register/invoke
pair, and the RPC-style request/response model is removed. Each broker owns its
own queue, so brokers can be paused and resumed independently.

Also fixes flaws found while reviewing the rewrite, each covered by tests:

• filters now AND their keys instead of OR
• each emit() call resolves to its own result rather than a shared promise
• invoke completion is the settling of each handler, not a finish() count, so a
  filtered-out or negligent handler can no longer hang or truncate the stream
• invoke gains an error channel: fail-loud by default, isolate with { onError }
• interceptor routing is cleaned up when a broker aborts
• queueMethod no longer resets a running queue

BREAKING CHANGE: the entire public API of @plugola/message-bus has changed.

• MessageBus is replaced by Bus; bus.broker(name) returns a PluginBroker.
• Events are classes implementing Event (or extending Invocation) and are
  subscribed to by class, not string name. EventDescriptions are removed.
• Invokables and generators are unified into a streaming API: register a handler
  with broker.register(Invocation, (event, { send, signal }) => ...) and call
  broker.invoke(new Invocation()).collect() / .iterate(). There is no
  finish() — a handler completes when it returns or its promise settles. The
  RPC-style request/response model is removed.
• Invocation errors are fail-loud by default; pass { onError } to invoke()
  to isolate handlers and keep the stream running.
• Lifecycle methods are renamed: start/stop are now resume/pause on both
  Bus and PluginBroker.
• CancelEvent is renamed to CANCEL.

Co-Authored-By: Claude Opus 4.8 (1M context) noreply@anthropic.com