branch-4.0: [fix](fe) Skip decommissioning BE for load

[liaoxin01]

Pick #65049

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Pull request overview

This PR tightens FE backend selection for load-related paths to exclude decommissioned/decommissioning BEs, preventing load tasks from being routed to BEs that are being removed from service.

Changes:

• Extend BeSelectionPolicy with needNonDecommissioned and make needLoadAvailable() imply non-decommissioned selection.
• Update backend selection logic for Stream Load, Routine Load, Group Commit, and Kafka meta requests to skip decommissioned/decommissioning BEs.
• Add/adjust unit tests to validate decommissioning-aware backend selection behavior.

Reviewed changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
fe/fe-core/src/test/java/org/apache/doris/system/SystemInfoServiceTest.java	Updates selection-policy tests to reflect “load available + non-decommissioned” behavior.
fe/fe-core/src/test/java/org/apache/doris/load/StreamLoadHandlerTest.java	Adds test ensuring Stream Load backend selection skips decommissioning backends.
fe/fe-core/src/test/java/org/apache/doris/load/routineload/RoutineLoadManagerTest.java	Updates mocks to satisfy new backend availability filtering in Routine Load manager logic.
fe/fe-core/src/test/java/org/apache/doris/load/routineload/RoutineLoadBackendSelectionTest.java	Adds tests covering Routine Load backend selection behavior with decommissioning/load-disabled backends.
fe/fe-core/src/main/java/org/apache/doris/system/BeSelectionPolicy.java	Adds needNonDecommissioned and integrates it into matching and toString().
fe/fe-core/src/main/java/org/apache/doris/load/StreamLoadHandler.java	Skips decommissioned/decommissioning BEs when selecting Stream Load backend in cloud mode.
fe/fe-core/src/main/java/org/apache/doris/load/routineload/RoutineLoadManager.java	Filters out load-unavailable and decommissioned/decommissioning BEs when computing per-BE capacity; refines reuse logic.
fe/fe-core/src/main/java/org/apache/doris/load/GroupCommitManager.java	Treats decommissioning backends as unavailable (not only in cloud mode) and improves error details.
fe/fe-core/src/main/java/org/apache/doris/datasource/kafka/KafkaUtil.java	Centralizes backend availability checks for Kafka meta requests and excludes decommissioning BEs.
fe/fe-core/src/main/java/org/apache/doris/cloud/load/CloudRoutineLoadManager.java	Uses load availability + non-decommissioned filtering for cloud routine load backend selection.

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[liaoxin01]

run buildall

[hello-stephen]

FE UT Coverage Report

Increment line coverage 46.67% (14/30) 🎉
Increment coverage report
Complete coverage report

[liaoxin01]

run buildall