Add injectable sleep_fn parameter to MockVWS

[adamtheturtle]

Summary

Implements issue #2919 by adding an injectable sleep_fn parameter to MockVWS. This allows callers to inject a custom delay strategy for testing timeout behavior without monkeypatching internals.

Changes

• Add sleep_fn: Callable[[float], None] = time.sleep parameter to MockVWS.__init__
• Pass the sleep function through _wrap_callback for both the timeout and success code paths
• Add two comprehensive tests verifying the injected function is called correctly on both paths
• Update CHANGELOG with feature description

Test plan

✓ All 6 existing and new response delay tests pass
✓ Custom sleep function is called with correct delay value on success path
✓ Custom sleep function is called with effective timeout on timeout path

🤖 Generated with Claude Code

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Note

Low Risk
Small, additive API change limited to test/mock timing behavior; primary risk is minor backward-compatibility/typing issues for callers constructing MockVWS.

Overview
MockVWS now accepts an injectable sleep_fn (defaulting to time.sleep) and threads it through the response-delay wrapper so both the timeout and successful delay paths use the provided sleep strategy instead of hardcoded sleeping.

Adds tests asserting the injected function is called with the configured delay or the effective timeout value, and documents the new parameter in CHANGELOG.rst.

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