[roll] Roll fuchsia [time] Escrow Inspect data in pull time sources

Transient time sources are launched by Timekeeper to provide a single
time sample and are then terminated. This lifecycle causes their
diagnostic (Inspect) data to be lost upon shutdown.

This change implements an Inspect escrow mechanism to preserve this
data for later analysis. The new flow is as follows:

- The `PullSource` FIDL protocol is updated to include a `Shutdown`
  method that returns an `EscrowToken`.
- Upon receiving a `Shutdown` request, the time source freezes its
  Inspect data using `inspect_runtime` to obtain an `EscrowToken`.
- This token is returned to the caller (Timekeeper).
- Timekeeper stores the token, ensuring the Archivist preserves the
  Inspect data even after the time source component has terminated.
- On the next sampling attempt, Timekeeper drops the previous token
  to allow resource cleanup before launching a new time source instance.

The change also introduces a `use_fake_sampler` configuration to the
HTTPS time source and adds an integration test to verify the escrow
behavior.

Original-Bug: b/367743262
Test: fx test httpsdate-time-source-tests
Test: fx test httpsdate-time-source-integration-tests
Original-Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/1404673
Original-Revision: c7c51fcd9d4aa05a017383481132aa2eed83ab38
GitOrigin-RevId: 256cd46b42511b28434ed538e30fb577cf2ab2d7
Change-Id: I14cef0c17abbe9e7815ba8930af3b353565d31d9