Add injectable delay strategy to MockVWS to remove test-time monkeypatching

[adamtheturtle]

Problem

MockVWS currently hardcodes time.sleep(...) inside _wrap_callback, which makes timeout-boundary tests in downstream projects slow and encourages monkeypatching internals.

Current behavior in mock_vws/_requests_mock_server/decorators.py:

• if delay_seconds > timeout: time.sleep(timeout) then raise requests.exceptions.Timeout
• else: callback + time.sleep(delay_seconds)

This is correct semantically, but not test-friendly.

Proposed solution (preferred)

Add a first-class, injectable delay function on MockVWS so tests can control virtual time without monkeypatching module internals.

API proposal

class MockVWS:
    def __init__(
        ...,
        response_delay_seconds: float = 0.0,
        sleep_fn: Callable[[float], None] = time.sleep,
    ) -> None:
        self._sleep_fn = sleep_fn

Then use self._sleep_fn(...) in _wrap_callback instead of direct time.sleep(...).

Optional enhancement

If needed, add clock_fn: Callable[[], float] = time.time for future elapsed-time-based delay logic.

Why this is better than an internal sleep loop

• Keeps default behavior exactly the same for normal users.
• Makes tests deterministic and fast without monkeypatching private module paths.
• Avoids tight coupling to freezegun internals.
• Works for both success and timeout branches.

Example downstream usage

with freeze_time() as frozen:
    mock = MockVWS(
        response_delay_seconds=31,
        sleep_fn=lambda s: frozen.tick(delta=datetime.timedelta(seconds=s)),
    )

Acceptance criteria

1. MockVWS accepts sleep_fn with default time.sleep.
2. Existing behavior remains unchanged when sleep_fn is not provided.
3. Existing tests pass unchanged.
4. Add one new test proving injected sleep_fn is called for both:
   • non-timeout delay path
   • timeout path (delay_seconds > effective timeout)
5. Docs/changelog mention test-time virtual delay support.

Non-goals

• No change to public timeout semantics.
• No forced dependency on freezegun.