ts-patch-3: time skipping halts when there are pending external transfer tasks (#10279)

## What changed?
When there are pending external transfer tasks (signals/cancellation),
time doesn't skip.

## Why?
1. This follows the foundational principle that time skipping only
occurs when there are no in-flight tasks.
2. In scenarios where a workflow selector is waiting on both a timer and
a SignalExternalWorkflow, the timer should not fire before the signal is
delivered — see the functional test added in this pr for a concrete
example.

## How did you test it?
- [x] built
- [x] run locally and tested manually
- [ ] covered by existing tests
- [x] added new unit test(s)
- [x] added new functional test(s)