branch-4.0:[feature](cloud) Support compaction read-write separation for cloud mode #60310

[Yukang-Lian]

Summary

Cherry-pick from #60310 (commit 5cbe1b4) to branch-4.0

• Implements compaction read-write separation for cloud mode so that only the cluster that last performed data load executes compaction, preventing file cache invalidation on read-only clusters
• Default is disabled (enable_compaction_rw_separation = false), can be enabled per-cluster via BE config

Conflict Resolution

• gensrc/proto/cloud.proto: TxnInfoPB field 21 (defer_deleting_pending_delete_bitmaps) does not exist on branch-4.0, only added load_cluster_id (field 22) from this PR

Key changes

• Track "last active cluster" per tablet in TabletStatsPB (updated during commit_txn)
• FE sets load_cluster_id in TxnInfoPB during begin_txn
• BE background thread caches cluster status via get_cluster_status RPC
• Skip compaction in get_topn_tablets_to_compact for tablets owned by other clusters
• Safety valve: force compaction when version count exceeds 80% of max
• Configurable takeover timeout when write cluster becomes unavailable

Test plan

• Unit tests: cloud_cluster_info_test, compaction_rw_separation_test
• Regression tests: test_compaction_rw_separation, test_compaction_cluster_takeover, test_compaction_rw_separation_disabled, test_compaction_rw_separation_force

[Thearas]

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Please clearly describe your PR:

1. What problem was fixed (it's best to include specific error reporting information). How it was fixed.
2. Which behaviors were modified. What was the previous behavior, what is it now, why was it modified, and what possible impacts might there be.
3. What features were added. Why was this function added?
4. Which code was refactored and why was this part of the code refactored?
5. Which functions were optimized and what is the difference before and after the optimization?

[Yukang-Lian]

run buildall

[doris-robot]

Cloud UT Coverage Report

Increment line coverage 51.72% (30/58) 🎉

Increment coverage report
Complete coverage report

Category	Coverage
Function Coverage	79.16% (1789/2260)
Line Coverage	64.43% (31982/49641)
Region Coverage	65.26% (16011/24533)
Branch Coverage	55.84% (8523/15264)

[hello-stephen]

FE UT Coverage Report

Increment line coverage 22.22% (2/9) 🎉
Increment coverage report
Complete coverage report

[hello-stephen]

BE UT Coverage Report

Increment line coverage 70.79% (143/202) 🎉

Increment coverage report
Complete coverage report

Category	Coverage
Function Coverage	52.97% (19227/36300)
Line Coverage	36.13% (179124/495760)
Region Coverage	32.77% (139035/424286)
Branch Coverage	33.71% (60310/178888)

[Yukang-Lian]

Superseded by #61920 (combined cherry-pick PR for branch-4.0)