Improve array validation and bound computationCache memory map size

[shenald-dev]

1. Added !Array.isArray(messages) validation to /v1/chat/completions: Hardens the API gateway by verifying that the messages attribute is not a string or another primitive, which could lead to application crashes when mapping over it.
2. Added a memory bound to computationCache Map: The heavyComputation benchmark previously cached elements infinitely based on incoming iterations, leading to a memory leak. Bounded this mapping to 1000 items, and clears it when exceeded to cap maximum memory size.
3. Appended an entry to .jules/bolt.md: Documented the array validation error and bounding Map limits for long-running processes for long-term historical context.

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PR created automatically by Jules for task 6403325572547754351 started by @shenald-dev

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