Delete unread NUM_PARTITIONS from ResourceConfig

[sjainit]

What

Removes the NUM_PARTITIONS field from ResourceConfig, continuing the ResourceConfig config-surface cleanup that makes IdealState the single source of truth for structural fields.

Why

The partition count on ResourceConfig has no readers:

• Every getNumPartitions() call in main source reads it off IdealState (ZKHelixAdmin ×2, ClusterStateVerifier) — never off ResourceConfig.
• There are no direct ResourceConfigProperty.NUM_PARTITIONS reads anywhere.
• JobConfig/WorkflowConfig (which extend ResourceConfig) don't touch it.

IdealState owns the partition count and has its own independent change detection via IdealStateTrimmer (whose non-trimmable set includes IdealStateProperty.NUM_PARTITIONS), so removing the ResourceConfig copy loses no signal.

Changes

Remove from ResourceConfig: the NUM_PARTITIONS enum constant, getNumPartitions() getter, Builder field + getNumPartitions/setNumPartitions, constructor param + field write, the validate() check, and the IdealState→ResourceConfig merge line. Also drop the NUM_PARTITIONS entry from ResourceConfigTrimmer's non-trimmable set, and remove vestigial setNumPartitions calls from tests.

Why dropping it from ResourceConfigTrimmer is safe

The change detector trims the raw persisted ResourceConfig (ResourceChangeSnapshot trims dataProvider.getResourceConfigMap()), not the IdealState-merged one. Production ResourceConfig ZNodes never persist NUM_PARTITIONS, so trimming it changes nothing; IdealState partition-count changes are still detected via the separate IdealState path.

Testing Done

• JDK 11: mvn -o -pl helix-rest -am test -Dtest=TestResourceConfig,TestClusterModelProvider,TestHelixPropoertyTimmer -Dsurefire.failIfNoSpecifiedTests=false — passes, including core and REST main/test compilation and all 23 selected test cases.
• Constructor coverage checks surviving fields and the absence of retired raw fields, including NUM_PARTITIONS. The IdealState merge regression retains coverage that existing raw group metadata is preserved.

Scope and related PRs

• Standalone on dev, which already includes merged Retire legacy WeightAwareRebalanceUtil, remove unread STATE_MODEL_DEF_REF/REPLICAS from ResourceConfig #270. Only NUM_PARTITIONS is removed here. HELIX_ENABLED, EXTERNAL_VIEW_DISABLED, MIN_ACTIVE_REPLICAS, and MAX_PARTITIONS_PER_INSTANCE remain available. This PR does not include or depend on the unmerged changes in Delete dead ResourceConfig HELIX_ENABLED and EXTERNAL_VIEW_DISABLED #268, Rewire minActiveReplica to IdealState and delete MIN_ACTIVE_REPLICAS from ResourceConfig #272, or Rewire maxPartitionsPerInstance to IdealState and delete MAX_PARTITIONS_PER_INSTANCE from ResourceConfig #273.
• Deprecate ResourceConfig.Builder structural setters that duplicate IdealState #262 (deprecates ResourceConfig.Builder structural setters) overlaps with the setNumPartitions setter deleted here and will need a rebase once this merges.

Co-authored-by: Copilot 223556219+Copilot@users.noreply.github.com

[LZD-PratyushBhatt]

wrong base branch, switch to dev. rebase the PR.

[LZD-PratyushBhatt]

one ask before the enum goes.

[LZD-PratyushBhatt]

can we get the usage count for NUM_PARTITIONS on ResourceConfig like we did for other PRs as well, just for bookkeeping? the trimmer side already looks fine since IdealStateTrimmer keeps NUM_PARTITIONS, so change detection will work still.

[sjainit]

No usage @LZD-PratyushBhatt, everybody sets it on IdealState