Implementation of 'connecting' sync status from Dart SDK

[LucDeCaf]

Implementation of the SyncStatus.connecting flag in the Dart SDK as SyncStatus.connecting() and SyncStatusOptions.connecting?: boolean in SyncStatusOptions.

NB: If connected === true then connecting === false always.

[changeset-bot]

🦋 Changeset detected

Latest commit: f1eb79c

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

This PR includes changesets to release 6 packages

Name	Type
@powersync/common	Minor
@powersync/op-sqlite	Patch
@powersync/react-native	Patch
@powersync/tanstack-react-query	Patch
@powersync/web	Patch
@powersync/diagnostics-app	Patch

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

[LucDeCaf]

Putting this here for myself later.

TODOS (all done now)

• Find all modifications to SyncStatus.connected and check if SyncStatus.connecting should also be modified
• Find all places where the shape of SyncStatus is important and check if it supports SyncStatus.connecting
• Build package and test SyncStatus.connecting