merge: catch up with main (raw change streams PR #591)

Merges upstream main which includes PR #591 (raw change streams) and
PR #599 (direct BSON Buffer -> JSON conversion).

Auth fix conflicts (types.ts, config.test.ts) resolved — both sides
had the same fix, upstream also added database name decoding.

ChangeStream.ts has 11 unresolved conflicts — PR #591 replaced the
MongoDB driver ChangeStream with a custom RawChangeStream using raw
aggregate + getMore. Our Cosmos DB changes need to be re-applied to
the new code structure. Resolved in the next commit.

resolve: ChangeStream.ts merge conflicts for raw change streams

Re-applied all Cosmos DB changes to the new raw change stream code
structure from PR #591. The raw aggregate approach is better for
Cosmos DB: no lazy ChangeStream init, explicit cursor management,
$changeStream stage built directly in pipeline.

Changes applied to new structure:
- detectCosmosDb() calls in getSnapshotLsn, initReplication, streamChangesInternal
- getEventTimestamp() adapted to ProjectedChangeStreamDocument type
- Sentinel checkpoint with BSON.deserialize for fullDocument (raw Buffer)
- Pipeline guards: skip $changeStreamSplitLargeEvent and showExpandedEvents
- Cluster-level aggregate (admin db + allChangesForCluster) when isCosmosDb
- startAtOperationTime fix (startAfter != null)
- Keepalive guard for Cosmos DB resume tokens
- .lte() dedup guard skip on Cosmos DB
- wallTime tracking for replication lag
- Added changeset for @powersync/service-module-mongodb (minor)

Verified: 59/59 standard MongoDB tests pass.
Cosmos DB cluster is currently down — tests blocked by TLS timeout.
Code audit of RawChangeStream.ts found no compatibility issues:
cursor ID type auto-fixed by BigInt, postBatchResumeToken needs
empirical verification when cluster is back.

Author: Sleepful

.changeset/bright-clouds-glow.md

@@ -0,0 +1,5 @@
+---
+'@powersync/service-module-mongodb': minor
+---
+
+Add experimental Cosmos DB MongoDB vCore support. Auto-detects Cosmos DB via `hello` command and applies workarounds for missing `clusterTime`, `operationTime`, and unsupported change stream features.

.changeset/calm-doors-shine.md

@@ -0,0 +1,5 @@
+---
+'@powersync/service-module-mongodb': minor
+---
+
+Use custom MongoDB change stream implementation to get better low-level control.

.changeset/chilled-bags-complain.md

@@ -0,0 +1,11 @@
+---
+'@powersync/service-module-postgres-storage': patch
+'@powersync/service-module-mongodb-storage': patch
+'@powersync/service-core-tests': patch
+'@powersync/service-module-postgres': patch
+'@powersync/service-core': patch
+'@powersync/service-sync-rules': patch
+'@powersync/lib-service-mongodb': patch
+---
+
+Add `config.storage_version` configuration option.