Allow configurable timeouts for PrepareData plugins

[LukeAVanDrie]

What would you like to be added:

Currently, the timeout for PrepareData plugins is hardcoded to 400ms in pkg/epp/handlers/director.go:

const prepareDataTimeout = 400 * time.Millisecond

This should be exposed via the Director configuration, potentially per-plugin or global.

Why is this needed:

Different plugins (e.g., semantic retrieval, RAG preprocessing) have vastly different latency profiles. A hardcoded 400ms is too aggressive for some and too loose for others.

[LukeAVanDrie]

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[k8s-ci-robot]

@LukeAVanDrie:
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[tsj-30]

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