[MongoDB] Track bytes, transactions and chunks replicated

[rkistner]

These replication metrics are being tracked for the various source databases:

Metric	PostgreSQL	MySQL	SQL Server	MongoDB
powersync_data_replicated_bytes_total	✅			🆕
powersync_rows_replicated_total	✅	✅	✅	✅
powersync_transactions_replicated_total	✅	✅	✅	🆕
powersync_chunks_replicated_total	✅			🆕
powersync_replication_lag_seconds	✅	✅		✅

This PR adds tracking of powersync_data_replicated_bytes_total and powersync_transactions_replicated_total.

Transactions replicated is informational only - it has no direct effect on performance and is not a good measurement of replication performance. It is however easy to track, and may give an indication of the write patterns on the source database.

Data replicated bytes can be a good indication of replication performance. If this metric is low while replication lag is building up, it gives an indication of a replication throughput issue, such as #573. Note that this is slightly different from bytes transferred over the network - the metric here is after decompression, and without TLS and other protocol overhead.

Chunks replicated is an internal metric in how the database batches the data. We don't directly replicate according to these chunks at the moment, but it could give useful info in some cases.

Unfortunately the byte tracking relies on internals in the MongoDB driver. We do test it properly, and gracefully handle cases where the properties are not present - for metrics it may be better to not have the metrics rather than have a hard failure. If we go with an approach such as #309 in the future, we should be able to remove these hacks.

[changeset-bot]

🦋 Changeset detected

Latest commit: 1477026

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 12 packages

Name	Type
@powersync/service-module-mongodb	Patch
@powersync/service-schema	Patch
@powersync/service-image	Patch
@powersync/service-core	Patch
@powersync/service-core-tests	Patch
@powersync/service-module-core	Patch
@powersync/service-module-mongodb-storage	Patch
@powersync/service-module-mssql	Patch
@powersync/service-module-mysql	Patch
@powersync/service-module-postgres-storage	Patch
@powersync/service-module-postgres	Patch
test-client	Patch

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