[Misc] Remove unused code and add missing @Override annotations (SonarCloud)

[vmassol]

Summary

Mechanical, behaviour-preserving cleanup of several SonarCloud rules across 24 modules (40 issues fixed in 27 files):

• java:S1068 — remove unused private fields
• java:S1481 / java:S1854 — remove unused local variables and their dead-store assignments (these fire as a pair on the same line)
• java:S1161 — add missing @Override annotations

Details

• Unused private fields (S1068): the field declaration (and its javadoc, if any) was removed. Where removal orphaned an import, that import was removed too (DocumentReference, RenderingContext, Logger/LoggerFactory, InternetAddress).
• Unused locals / dead stores (S1481 + S1854): when the right-hand side was a pure expression the whole declaration was removed; when it had a side effect that must be kept (e.g. newXObject(...), assertThrows(..., ...)), only the Type name = prefix was stripped so the call remains a bare statement.
• Missing @Override (S1161): the annotation was added above the flagged method signatures. Purely additive.

No functional/behavioural change: unused code removal and annotation additions only.

A handful of remaining S1068 issues were intentionally left out because they are write-only fields assigned in multiple places (removing the declaration alone would not compile) — those need a non-mechanical change and are out of scope here.

Test plan

• mvn clean install -Plegacy,snapshot -DskipTests across all 24 affected modules in one reactor — BUILD SUCCESS. Test sources still compile and Checkstyle passes; the changes are behaviour-preserving.

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