More checksum calculation fixes

[rkistner]

#351 fixed some checksum-related issues, but introduced others.

These were cases not caught by the current tests, since it did not fully cover all cases of partial checksum responses. My manual testing did also not pick this up since I mostly focused on testing a single large bucket. New tests cover this properly now. The tests depend on random ordering on MongoDB so individual tests were not failing consistently, but combining them all it did always cause some failures at least.

This was caused by two issues:

1. A batchCount++ that should never have been there.
2. Assuming $group results will be sorted if the input is sorted - that was not the case.

This fixes it.

[changeset-bot]

🦋 Changeset detected

Latest commit: ed336fd

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

This PR includes changesets to release 11 packages

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

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[simolus3]

The fix and associated tests make sense to me 👍