…) (#190)

Replace std::this_thread::sleep_for with deterministic event-based
synchronization primitives to improve test stability and eliminate flakiness.

Changes:
- integration_tests/failures/error_handling_test.cpp:
  - Replace sleep_for(10ms) with wait_for_condition for event processing

- integration_tests/scenarios/event_bus_integration_test.cpp:
  - Replace 5 sleep_for(10ms) calls with wait_for_condition using
    atomic predicates
  - Use yield() for unsubscribe verification (negative test)

- integration_tests/scenarios/full_system_integration_test.cpp:
  - Replace 2 sleep_for(1ms) rate limiters with yield()
  - Replace 2 sleep_for(50ms) waits with wait_for_condition

- integration_tests/scenarios/runtime_binding_integration_test.cpp:
  - Replace sleep_for(100μs) with yield() for thread coordination

- tests/config_watcher_test.cpp:
  - Remove unnecessary sleep before file modification test
  - Replace sleep_for(1ms) rate limiter with yield()

The following sleep_for usages were intentionally kept as they serve
specific test purposes:
- Stress tests with intentional duration-based execution
- Mock executor delay implementations
- Simulated slow factory calls for concurrency testing
- Race condition simulation for shutdown tests

Verified: All 92 integration tests pass with --gtest_repeat=10