[FEATURE] Avoid a single function stuck forever

[badmonster0]

Sometimes a single function can be stuck for a really long time, e.g. Ollama (bug). Our users experienced it and described in #656.

• If a function takes really long time (e.g. more than 30s), log a warning with specific function name.
• Each function may have a timeout (we can start from 300s as default, don't want it to be too short as some functions indeed needs long time sometimes, e.g. some PDF parsing; and each function can override it, similar to the setting to enable cache). We abort the function and return an error if timeout.

Side note: in the future we also want to expose more metrics/stats and allow users to inspect pending functions in cocoinsight

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