[To dev/1.3] Pipe: dynamically share idle floating memory (#18422)

[Caideyipi]

Summary

• Backport commit 10950e1 (Pipe: dynamically share idle floating memory with TsFile sync #18422) to dev/1.3.
• Treat pipe_total_floating_memory_proportion as the upper limit for floating InsertNode memory.
• Allow non-floating Pipe allocations to borrow unused floating memory and reclaim it symmetrically.
• Adapt the change to dev/1.3's counter-based PipeMemoryManager and update capacity consumers to use the manager instance.
• Preserve the dev/1.3 resize admission hard limits and add regression coverage.

Testing

• Spotless apply for datanode and node-commons: passed.
• DataNode test-compile with Checkstyle and Spotless: passed.
• PipeMemoryManagerResizeTest, PipeMemoryManagerTest, and PipeDataNodeTaskAgentTest: 12 tests, 0 failures, 0 errors.
• git diff --check origin/dev/1.3...HEAD: passed.