[fix][broker] transitivity violation during bundle comparison in topK bundles by NamespaceBundleStats,BundleData Comparator

[Meet0861]

Fixes: #24754

Motivation

The topK bundle selection fails due to the sorting failure in the partition sort algo being used here.
Partition sort uses, NamespaceBundleStats' + BundleData's custom ccompararable implementations where it checks throughput, connections, cache size etc against the defined threshold and when values are within the defined thresholds, they are considered "equal" (return 0), but this creates transitivity violations.
It violates the transitivity property required by Java's Comparable interface, causing Collections.sort() to potentially throw IllegalArgumentException with "Comparison method violates its general contract" error.
Error Log:
2025-09-12T22:29:58.832386492+05:30 16:59:58.832 [pulsar-load-manager-1-1] WARN org.apache.pulsar.broker.loadbalance.LoadResourceQuotaUpdaterTask - Error write resource quota - java.lang.IllegalArgumentException: Comparison method violates its general contract

Due to this failure, the job - writeBundleDataOnZooKeeper(leader broker writes bundle data aggregated from all brokers to metadata store) in modularLoadManager may fail link and can cause degradation in productions due to failure/inconsistencies in LB decisions

Modifications

added strict NamespaceBundleStats comparator and BundleData comparator to be used for sorting for topk bundle comparison which is being used by ModularLoadManager and ExtensibleLoadManager

Verifying this change

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This change added tests and can be verified as follows:

• Added unit tests to validate the fix

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Documentation

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Matching PR in forked repository

PR in forked repository: https://github.com/Meet0861/pulsar/tree/fix-transitivityViolationInNamespaceBundleStatsAndBundledataComparator

[github-actions]

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[lhotari]

@Meet0861 Pull requests should target the master branch. I changed the base, but that messed up things. You can rebase on your side and do a force-push. One way is to do this is:

git fetch origin # assuming "origin" is apache/pulsar
git reset --hard origin/master
git cherry-pick 8ce1fc4 # your PR commit

then push changes to the PR branch

[lhotari]

@Meet0861 Thanks for the effort of debugging and drilling down to the root cause.
Since the compareTo contracts were violated in NamespaceBundleStats, TimeAverageMessageData and ResourceUnitRanking classes, I have addressed those in an alternative approach to address the issue, #24772. It wouldn't have been useful to keep the invalid implementations since they could have caused similar problems in the future when sorting would have been used. The main purpose of compareTo methods is sorting.
The original reason for the Math.abs was to compare with a coarse granularity (or resolution). I have addressed that without Math.abs in the PR so that the value is divided by the comparison resolution/granularity at comparison. The behavior isn't exactly the same as Math.abs, but it does retain the behavior of comparing at the desired level of granularity.
Since the compareTo methods are now fixed with #24772, it won't be necessary to have custom comparators that this PR provides.