HDFS-17949. Add optional FedBalance content summary verification

[qijiale76]

Description of PR

This PR adds an optional FedBalance verification phase after the final DistCp succeeds.

The verification is disabled by default. When enabled, FedBalance compares the source and destination ContentSummary directory count, file count, and length after excluding snapshot content. A mismatch fails the job, while transient ContentSummary read failures are retried by the procedure scheduler.

This provides a lightweight built-in verification mechanism without changing the default FedBalance behavior.

How was this patch tested?

Ran FedBalance unit tests locally and validated on a production cluster.

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[hadoop-yetus]

💔 -1 overall

Vote	Subsystem	Runtime	Logfile	Comment
+0 🆗	reexec	6m 55s		Docker mode activated.
			_ Prechecks _
+1 💚	dupname	0m 0s		No case conflicting files found.
+0 🆗	codespell	0m 0s		codespell was not available.
+0 🆗	detsecrets	0m 0s		detect-secrets was not available.
+0 🆗	xmllint	0m 0s		xmllint was not available.
+0 🆗	markdownlint	0m 0s		markdownlint was not available.
+1 💚	@author	0m 0s		The patch does not contain any @author tags.
+1 💚	test4tests	0m 0s		The patch appears to include 2 new or modified test files.
			_ trunk Compile Tests _
+0 🆗	mvndep	2m 1s		Maven dependency ordering for branch
+1 💚	mvninstall	28m 28s		trunk passed
+1 💚	compile	9m 30s		trunk passed with JDK Ubuntu-21.0.11+10-1-24.04.2-Ubuntu
+1 💚	compile	9m 45s		trunk passed with JDK Ubuntu-17.0.19+10-1-24.04.2-Ubuntu
+1 💚	checkstyle	3m 22s		trunk passed
+1 💚	mvnsite	1m 26s		trunk passed
+1 💚	javadoc	1m 17s		trunk passed with JDK Ubuntu-21.0.11+10-1-24.04.2-Ubuntu
+1 💚	javadoc	1m 14s		trunk passed with JDK Ubuntu-17.0.19+10-1-24.04.2-Ubuntu
-1 ❌	spotbugs	0m 41s	/branch-spotbugs-hadoop-tools_hadoop-federation-balance-warnings.html	hadoop-tools/hadoop-federation-balance in trunk has 12 extant spotbugs warnings.
+1 💚	shadedclient	17m 21s		branch has no errors when building and testing our client artifacts.
			_ Patch Compile Tests _
+0 🆗	mvndep	0m 18s		Maven dependency ordering for patch
+1 💚	mvninstall	0m 51s		the patch passed
+1 💚	compile	9m 6s		the patch passed with JDK Ubuntu-21.0.11+10-1-24.04.2-Ubuntu
+1 💚	javac	9m 6s		the patch passed
+1 💚	compile	10m 3s		the patch passed with JDK Ubuntu-17.0.19+10-1-24.04.2-Ubuntu
+1 💚	javac	10m 3s		the patch passed
+1 💚	blanks	0m 0s		The patch has no blanks issues.
+1 💚	checkstyle	3m 14s		the patch passed
+1 💚	mvnsite	1m 35s		the patch passed
+1 💚	javadoc	1m 17s		the patch passed with JDK Ubuntu-21.0.11+10-1-24.04.2-Ubuntu
+1 💚	javadoc	1m 16s		the patch passed with JDK Ubuntu-17.0.19+10-1-24.04.2-Ubuntu
+1 💚	spotbugs	2m 22s		the patch passed
+1 💚	shadedclient	18m 26s		patch has no errors when building and testing our client artifacts.
			_ Other Tests _
+1 💚	unit	1m 46s		hadoop-federation-balance in the patch passed.
+1 💚	unit	38m 25s		hadoop-hdfs-rbf in the patch passed.
+1 💚	asflicense	0m 49s		The patch does not generate ASF License warnings.
		179m 22s

Subsystem	Report/Notes
Docker	ClientAPI=1.55 ServerAPI=1.55 base: https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-8582/1/artifact/out/Dockerfile
GITHUB PR	#8582
Optional Tests	dupname asflicense compile javac javadoc mvninstall mvnsite unit shadedclient spotbugs checkstyle codespell detsecrets xmllint markdownlint
uname	Linux a26e41f563f1 5.15.0-179-generic #189-Ubuntu SMP Tue May 5 18:20:56 UTC 2026 x86_64 x86_64 x86_64 GNU/Linux
Build tool	maven
Personality	dev-support/bin/hadoop.sh
git revision	trunk / ff01a44
Default Java	Ubuntu-17.0.19+10-1-24.04.2-Ubuntu
Multi-JDK versions	/usr/lib/jvm/java-21-openjdk-amd64:Ubuntu-21.0.11+10-1-24.04.2-Ubuntu /usr/lib/jvm/java-17-openjdk-amd64:Ubuntu-17.0.19+10-1-24.04.2-Ubuntu
Test Results	https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-8582/1/testReport/
Max. process+thread count	3582 (vs. ulimit of 10000)
modules	C: hadoop-tools/hadoop-federation-balance hadoop-hdfs-project/hadoop-hdfs-rbf U: .
Console output	https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-8582/1/console
versions	git=2.43.0 maven=3.9.15 spotbugs=4.9.7
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