Use repository paging for statement retrieval

[thomasturrell]

Summary

• add a stored timestamp column to statements for efficient ordering and filtering
• paginate statement retrieval directly in the repository using sorted slices and page-based tokens
• persist stored timestamps when saving single or multiple statements

Testing

• ./mvnw -pl samples/xapi-server test (fails: wget cannot fetch Maven distribution in this environment)

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Codex Task

[thomasturrell]

@copilot can you fix up this pr so that it builds and the tests run

[Copilot]

@thomasturrell I've opened a new pull request, #405, to work on those changes. Once the pull request is ready, I'll request review from you.

[thomasturrell]

@copilot can you take another look at this pull request. Use maven clean install first to understand the current state

[Copilot]

@thomasturrell I've opened a new pull request, #406, to work on those changes. Once the pull request is ready, I'll request review from you.

[sonarqubecloud[bot]]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud