Introduce Credential Activity History Store

[ketzusaka]

Introduces a sharable on-device store for Android and iOS to retain credential activity. We're re-using some components from the Wallet storage here, while maintaining a separate database for the local activity as it is a separate concern and should never be backed up with the existing systems.

I've modeled the changes after how I typically use rust; mod.rs is mainly imports with most of the code in dedicated files, and tests in their related files.

This system is expected to evolve over time so i've prioritized a sensible migration strategy as part of these changes.

Tested integration on iOS. Will do Android later and follow up with any PRs that might be necessary for their integration. No runtime differences until the host apps are updated to use the new system.

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Note

Medium Risk
Touches encrypted cache schema/migration and new persisted user-activity data; incorrect migration or reset behavior could drop or leak history, but changes are well-tested and isolated from the credential vault.

Overview
Adds persistent credential activity history in the encrypted cache database so host apps can record proof-share outcomes (protocol, RP, client id, issuer schemas, terminal outcome, and optional failure reason).

CredentialStore gains record_activity, paginated list_activities, activity_metadata, and clear_activities, plus a UniFFI ActivityChangedListener (background thread, same pattern as vault changes) fired only on successful record/clear. New ActivityEntry / outcome types are exported for bindings.

Cache schema now creates an activity_entries table (indexed by created_at) via ensure_activity_schema, applied on every open—including after a disposable cache_entries wipe on schema version mismatch—so activity history is intended to outlive TTL cache resets while session seeds and similar rows are cleared.

Inserts enforce failure_reason only when outcome is Failed. ActivityQuery is a stub for future filtering. Small walletkit-sqlite addition: Transaction::query_row_optional.

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[paolodamico]

@Dzejkop let's keep this in the backlog for how to overall improve the listener experience, the risk of deadlocking here or other nasty stuff crossing the boundaries often is high

[paolodamico]

this is confusing, can we overall revise the doc comment here? it's hard to parse

[paolodamico]

high impact. not a blocker for this PR, but I strongly suggest that when parsing fails for corrupted entries, you delete the corrupted entry instead of erroring on the whole thing. with the current version, a single corrupted entry makes the history useless.