HDDS-16127. Document that OmKeyInfo holds a single key version

[chihsuan]

What changes were proposed in this pull request?

An earlier revision of this PR made ozone admin om quota repair version-aware, so that a key retaining more than one keyLocationVersions group was recounted per version instead of collapsing to the latest dataSize.

Per review on the Jira, no write path exercises bucket versioning today, and object versioning (HDDS-15728) keeps each object version in its own OmKeyInfo rather than adding groups here. The recount would therefore never run.

This revision drops the QuotaRepairTask change and records the invariant on the field instead, so the next reader does not have to re-derive it:

/**
 * Block locations of the key, one group per key version. No write path produces more than one group today, so a
 * key holds a single version and {@code dataSize} covers all of its blocks. Object versioning (HDDS-15728) keeps
 * each object version in its own OmKeyInfo rather than adding groups here.
 */
private List<OmKeyLocationInfoGroup> keyLocationVersions;

What is the link to the Apache JIRA?

https://issues.apache.org/jira/browse/HDDS-16127

How was this patch tested?

Javadoc only, no behavior change.

mvn -pl :ozone-common compile -DskipShade -DskipRecon -DskipDocs
./hadoop-ozone/dev-support/checks/checkstyle.sh

Generated-by: Claude Code (Opus 5)