HBASE-30226 Avoid same-row reverse FuzzyRowFilter hints

[EungsopYoo]

Why

Reverse FuzzyRowFilter can stop making progress when the reverse seek hint is equal to the current row. See HBASE-30226 for the detailed reproduction and analysis.

What

This PR keeps the HBASE-28634 reverse hint adjustment for the normal case, but avoids returning the adjusted hint when it is equal to the current row.

It also adds an end-to-end regression test for the abc -> abb -> aaa reverse scan case.

Test plan

mvn -pl hbase-server -am
-Dtest=TestFuzzyRowFilter,TestFuzzyRowFilterEndToEnd,TestFuzzyRowFilterEndToEndLarge,TestFuzzyRowAndColumnRangeFilter,TestFilterSerialization
-DexcludedGroups=slow -Dwarbucks.skip=true test

Result: Tests run: 68, Failures: 0, Errors: 0, Skipped: 0

mvn -pl hbase-rest -am -Dtest=TestScannersWithFilters -DexcludedGroups=slow -Dwarbucks.skip=true test

Result: Tests run: 12, Failures: 0, Errors: 0, Skipped: 0

[Copilot]

Pull request overview

This PR addresses a reverse-scan edge case in FuzzyRowFilter where a reverse seek hint can equal the current row, causing the scan to stop making progress (HBASE-30226). It refines the reverse-hint adjustment logic and adds a regression test to cover the problematic reverse scan sequence.

Changes:

• Prevent returning an adjusted reverse hint when it equals the current row, returning the unadjusted candidate instead.
• Update unit test expectations for reverse getNextForFuzzyRule behavior to reflect the new non-stalling hint.
• Add an end-to-end regression test covering the abc -> abb -> aaa reverse scan progression case.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
hbase-client/src/main/java/org/apache/hadoop/hbase/filter/FuzzyRowFilter.java	Adjust reverse hint computation to avoid same-row hints that can stall reverse scans.
hbase-server/src/test/java/org/apache/hadoop/hbase/filter/TestFuzzyRowFilter.java	Update reverse hint unit test expectations to ensure hints move backward when needed.
hbase-server/src/test/java/org/apache/hadoop/hbase/filter/TestFuzzyRowFilterEndToEnd.java	Add an end-to-end regression test for reverse scan progress under FuzzyRowFilter.

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