chasm: persist links and user_metadata at framework level

[Quinn-With-Two-Ns]

What changed?

Add per-request links (keyed by request_id) and user_metadata fields to ChasmComponentAttributes so any CHASM component can store them uniformly without each library defining its own proto field. This first PR just adds support, I will open up follow up PRs to update any existing components use these new fields.

Why?

Per the discussion here we think links and user metadata will be common components across CHASM components so it makes sense for the framework to handle this for us vs each component implementing it themselves.

How did you test it?

• built
• run locally and tested manually
• [] covered by existing tests
• added new unit test(s)
• added new functional test(s)

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Note

Medium Risk
Touches persisted CHASM component attributes and transaction close/replication paths; changes are additive and well-tested but affect core execution state layout.

Overview
Adds framework-level persistence for per-request links and user metadata on any CHASM component via new ChasmComponentAttributes fields (requests keyed by request_id, plus user_metadata).

MutableContext gains SetRequestLinks / SetUserMetadata; Context gains Links, RequestLinks, and UserMetadata. Writes are staged on the tree and flushed into component attributes during CloseTransaction (including versioned-transition bumps and replication updates). Reads prefer in-transaction pending values over persisted data; empty request_id is rejected; metadata for unregistered components is dropped with a warning.

Mocks and unit tests cover dirty-state, replace/remove semantics, and cross-transaction persistence. No individual CHASM libraries are migrated yet.

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