feat: Persist destination write stream state

[1neoneo3]

What

Adds durable destination write stream state to the replication store.

This PR introduces a small store-level foundation that lets a destination persist the state of an external write stream, including:

• the destination stream name
• the next offset to use
• creation and update timestamps

The implementation is wired through:

• the Postgres-backed store
• the in-memory store
• the notifying test store wrapper
• the error-reporting state store wrapper
• a Postgres migration for the new destination_write_streams table
• store-level tests for create/read/update/reset behavior

Why

BigQuery Storage Write API committed streams need a stable stream name and durable offsets to make retries safe.

Without persisted offsets, a destination can append the same logical rows again after a retry or process restart. This state store is the foundation needed by #875 to use BigQuery committed streams safely for append-only history writes.

Relationship to the follow-up PR

This is the first PR in the split for #873.

• feat: Persist destination write stream state #874: generic destination write stream state foundation
• feat: Add BigQuery append-only history mode #875: BigQuery append-only history mode using this state with Storage Write committed streams

Keeping this as a separate PR makes the storage contract reviewable without the larger BigQuery append-only implementation in the same diff.

Behavior and compatibility

• This PR does not change existing destination write behavior by itself.
• Existing destinations are not required to use the new state API.
• The new Postgres table is additive.
• In-memory and notifying stores are updated so existing tests and future destination tests can use the same store contract.
• Reset-for-resync clears in-memory destination write stream state, matching the Postgres store behavior.

Tests

• cargo check -p etl --features test-utils
• cargo check -p etl-replicator --no-default-features
• cargo test -p etl --features test-utils reset_for_resync_clears_destination_write_stream_state --test main

Refs #873

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[1neoneo3]

This PR is the first foundation slice for #873. It only adds durable destination write stream state and does not enable the BigQuery append-only mode by itself. #875 is stacked on top as the follow-up implementation.

[iambriccardo]

Thanks for the PR! We are currently thinking internally on how we want to add arbitrary metadata for destinations to store. Since it's hard to predict what each destination will need, we were thinking of going towards a design where any destination can store arbitrary data into the store.