fix: dispose call args on all failure paths per new StubHook ownership contract - #241

…ind queued calls

PromiseStubHook.call() and .stream() deep-copy their arguments before
chaining on the backing promise, but if that promise rejects, the copies
were never disposed, leaking any stubs they contained.

PromiseStubHook.dispose() also had a fast path that disposed the
resolution synchronously once available. A call chained on the promise
just before disposal could then be delivered after its target was
already disposed, violating ordering. Disposal now always chains on the
promise so it stays behind previously queued calls.

- RpcImportHook: collapse the three hand-rolled getEntry() guards in
  call()/stream()/map() into a private getEntryTakingOwnership() helper.
- ValueStubHook.map(): flatten the nested try/catch into a single catch that
  disposes captures defensively (dispose() is idempotent), matching call()'s
  flat shape.
- Tests: SyncThrowingHook extends ErrorStubHook instead of hand-stubbing all
  eight abstract StubHook methods.
- Condense the changeset to changelog style.

- Revert the mapImpl placeholder change: the stubs are always replaced at
  startup, so handling disposal there is dead code.
- ValueStubHook.map(): restore the narrow inner catch. Once ownership of the
  captures transfers to the delegate or applyMap(), disposing them in the
  outer catch is incorrect (a partially-completed callee may hold live
  references, e.g. hooks stored in the export table).
- Changeset: drop implementation details from the changelog entry.