Add adaptive test timeout utilities

[leynos]

Summary

• add smart timeout calculators with progressive retries
• switch daemon tests to adaptive timeouts
• document adaptive test timeout helper

Testing

• make fmt
• make lint
• make markdownlint
• make test

closes #71

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https://chatgpt.com/codex/tasks/task_e_68a4a71d79008322b249d6cf364c9ae1

Summary by Sourcery

Introduce adaptive timeouts with progressive retry support to daemon tests by adding a smart_timeouts module and timeout_with_retries helper, refactor existing tests to use these adaptive settings, remove legacy coverage-based multipliers, and document the new utilities.

New Features:

• Add smart_timeouts module with TimeoutConfig and TestComplexity to compute adaptive durations
• Implement timeout_with_retries helper to run operations with progressive timeout attempts

Enhancements:

• Refactor daemon tests to replace fixed timeouts and coverage detection logic with adaptive timeouts and retries
• Define constants for common test scenarios (DRAINED_NOTIFICATION, WORKER_SUCCESS, WORKER_ERROR)

Documentation:

• Add docs/adaptive-timeouts.md to explain usage of adaptive timeout utilities

Tests:

• Update existing async tests to use timeout_with_retries and smart_timeouts constants instead of manual tokio::timeout calls and coverage multipliers