test(emulator): increase coverage for timing.ts and memory.ts

[groupsky]

Description

Increase test coverage for timing.ts and memory.ts to meet the 95% threshold for all metrics.

Current Coverage

File       | % Stmts | % Branch | % Funcs | % Lines | Uncovered Lines
-----------|---------|----------|---------|---------|----------------
timing.ts  |  14.28% |    0.00% |   0.00% |  14.28% | (needs testing)
memory.ts  |  33.33% |    0.00% |   0.00% |  33.33% | (needs testing)

Note: These files are currently imported and tested via integration tests, but lack dedicated unit tests covering all code paths.

Acceptance Criteria

• timing.ts reaches 95% coverage (all metrics)
• memory.ts reaches 95% coverage (all metrics)
• Tests follow TDD principles (behavior-focused, clear, maintainable)
• Tests cover all code branches and edge cases
• Tests are co-located (timing.test.ts, memory.test.ts)
• All tests pass
• No regression in existing tests

Investigation Needed

Before implementing, investigate:

1. What functionality in these files is currently untested?
2. Are these files primarily tested via integration tests?
3. Should unit tests be added, or is integration testing sufficient?
4. Are there dead code paths that should be removed?

Related

• Identified in code review as pre-existing technical debt
• Not blocking for feat(emulator): implement TCP transport #252 or refactor(emulator): extract Modbus protocol helpers from transports #266

[groupsky]

✅ VERIFIED FIXED: timing.ts has comprehensive coverage in behaviors/timing.test.ts (406 lines) testing command detection delay, processing delay, per-register delay, transmission delay, realistic scenarios, and total delay calculation. memory.ts has full coverage in transports/memory.test.ts (75 lines) testing lifecycle, request/response handling, and error handling.