Fix readTransaction errors on node and op-sqlite drivers

[simolus3]

Currently, we run a BEGIN IMMEDIATE statement to start transactions (both readonly and readwrite). Technically, we're not really supposed to use BEGIN IMMEDIATE for readonly transactions since that statement is documented as taking a write lock, but for readonly connections in WAL mode it's still very convenient because there it uses the current state of the database as a snapshot. This has benefits over a regular BEGIN because writes between the start of the readonly transaction and its first statement would not be seen (ensuring the entire readTransaction block forms a logical transaction).

If we use readwrite connections with pragma query_only = TRUE however, attempting to use BEGIN IMMEDIATE throws and we shouldn't do it. So, this PR:

1. Changes the Node SDK to use readonly connections instead of the pragma query_only workaround.
2. Changes the common package to avoid BEGIN IMMEDIATE for connections using the pragma query_only = TRUE workaround (which is the case for op-sqlite which can't open actual readonly connections).
3. Adds tests for both behaviors to the node, op-sqlite and web pacakges.

[changeset-bot]

🦋 Changeset detected

Latest commit: 12c4def

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

This PR includes changesets to release 8 packages

Name	Type
@powersync/node	Patch
@powersync/common	Patch
@powersync/op-sqlite	Patch
@powersync/adapter-sql-js	Patch
@powersync/react-native	Patch
@powersync/tanstack-react-query	Patch
@powersync/web	Patch
@powersync/diagnostics-app	Patch

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[stevensJourney]

These changes look good to me