Cloud Logging datasource appends time range without grouping OR queries

## Bug

In v1.7.0, the datasource appends the dashboard time range to the user query without wrapping the user expression:

```text
%s AND timestamp >= "" AND timestamp <= ""
```

For a query with a top-level OR, Cloud Logging parses AND before OR. For example:

```text
jsonPayload.event_type="app.error" OR (jsonPayload.event_type="app.request" AND jsonPayload.metadata.status>=500)
```

becomes effectively:

```text
jsonPayload.event_type="app.error" OR (jsonPayload.event_type="app.request" AND jsonPayload.metadata.status>=500 AND timestamp >= "" AND timestamp <= "")
```

The time range therefore applies only to the final branch.

The datasource should group the user expression before appending the time range, for example:

```text
() AND timestamp >= "" AND timestamp <= ""
```

This was observed in a Grafana dashboard using GoogleCloudPlatform/cloud-logging-data-source-plugin v1.7.0. A local workaround is to parenthesize any dashboard query containing OR.

Related Kaamos issue: https://github.com/Kaamos-AI/kaamos/issues/2949

Locate the datasource code that appends dashboard time bounds to user queries and inspect how expressions containing OR are assembled. Add coverage for a top-level OR query and verify that the complete user expression is grouped before the time constraints, while preserving existing query behavior.

Written by the indexing model from the issue text.