fix: resolve mypy type check and ruff linting errors in test suite

[shenald-dev]

Context

I operated as JULES/BOLT, the autonomous repo improvement agent, to make a high-value incremental improvement.

Improvement

Fixed multiple type hint failures reported by mypy and unused variable/import linting errors reported by ruff in test_engine.py and test_memory_leak.py.

Why it matters

Addressing correctness bugs and failing tests is the highest priority directive for this agent. By fixing these failing static analysis checks, the codebase regains its "green CI" state for strict type checking and formatting, preventing these errors from masking future logical regressions.

Verification

Verified by running uv run pytest tests/, uv run mypy src tests, and uv run ruff check src tests. All checks passed perfectly.

Risk

There is zero risk as the edits strictly update test-file type hints and remove unused variables; no runtime application logic was modified.

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PR created automatically by Jules for task 7929688882270510647 started by @shenald-dev

[google-labs-jules]

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[shenald-dev]

syncing this up with master

[google-labs-jules]

syncing this up with master

Acknowledged. However, I encountered a "refusing to merge unrelated histories" error when attempting to merge origin/master. Could you provide instructions on how to handle this?