CPD: remove the 421 duplicated lines shared by FullSensorRecord, CompactSensorRecord and EventOnlyRecord #115

CPD (copy/paste detector, mvn pmd:cpd with the CI configuration minimumTokens=50, PMD 7.7.0 on commit 255b812) reports 9 duplicated blocks, 421 duplicated lines. Almost all of it is the three sensor-record decoders copying each other.

Duplications

Per pair: Compact ↔ Full 163 lines, Compact ↔ EventOnly 119 lines, EventOnly ↔ Full 99 lines.

Why it matters beyond the metric

FullSensorRecord, CompactSensorRecord and EventOnlyRecord share the same SDR "sensor record header" (owner ID/LUN/channel, sensor number, entity ID/instance, sensor type, event/reading type, ID string) plus the same getters/setters, but each has its own copy. Several of the decoding bugs found in the October 2026 review have to be fixed three times because of this (sensor owner/LUN handling #84, locator/ID-string parsing #86, reserved enum values #87), and the share-count expansion (#100) would have to be implemented twice.

Suggested fix

• Extract the common sensor-record header fields and their parsing into an intermediate abstract class (e.g. AbstractSensorRecord extends SensorRecord) used by the three record types; keep only the type-specific bytes (thresholds/units/linearisation for Full, sharing for Compact/EventOnly) in the subclasses.
• Fold the 22-line and 18-line blocks (GetSdrRepositoryInfo/ReadFruData timestamp-or-size parsing, GetSelEntry/SetSessionPrivilegeLevel response handling) into helpers in IpmiCommandCoder/TypeConverter.
• Add pmd:cpd-check to the verify phase so new duplication fails the build.