[to dev/1.3] Add copy fallback for compaction hard links

[shuwenwei]

Description

Backport of #18045 to dev/1.3.

This PR adds a shared FileUtils.createLink(..., fallBackToCopy) helper and uses it in compaction-related file linking paths.

When hard-link creation is unsupported or fails, these paths now fall back to copying the source file instead of failing immediately.

Changes

• Add a FileUtils.createLink(Path, Path, boolean) helper with optional copy fallback.
• Use the helper in compaction target preparation paths.
• Replace remaining compaction hard-link calls with the helper, including recovery tests.

Verification

• Searched compaction sources/tests for remaining Files.createLink / createHardlink usage; none remain.
• Compile/build checks were not run per instruction.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[codecov]

Codecov Report

❌ Patch coverage is 70.37037% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 43.07%. Comparing base (9b124e4) to head (324345f).

Files with missing lines	Patch %	Lines
...java/org/apache/iotdb/commons/utils/FileUtils.java	72.72%	3 Missing ⚠️
...paction/execute/task/InnerSpaceCompactionTask.java	60.00%	2 Missing ⚠️
...xecute/task/InsertionCrossSpaceCompactionTask.java	60.00%	2 Missing ⚠️
...gine/dataregion/modification/ModificationFile.java	0.00%	1 Missing ⚠️

Additional details and impacted files

@@              Coverage Diff              @@
##             dev/1.3   #18083      +/-   ##
=============================================
- Coverage      43.07%   43.07%   -0.01%     
  Complexity       198      198              
=============================================
  Files           3626     3626              
  Lines         242522   242533      +11     
  Branches       29582    29583       +1     
=============================================
- Hits          104473   104468       -5     
- Misses        138049   138065      +16     

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.