Add copy fallback for compaction hard links

[shuwenwei]

Description

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.
• Use the helper when linking TsFile resources and modification files.

[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 82.60870% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 41.31%. Comparing base (7f41f06) to head (c5800b9).

Files with missing lines	Patch %	Lines
...java/org/apache/iotdb/commons/utils/FileUtils.java	72.72%	3 Missing ⚠️
...dataregion/modification/v1/ModificationFileV1.java	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master   #18045      +/-   ##
============================================
- Coverage     41.42%   41.31%   -0.12%     
  Complexity      318      318              
============================================
  Files          5282     5282              
  Lines        369246   369257      +11     
  Branches      47786    47787       +1     
============================================
- Hits         152978   152555     -423     
- Misses       216268   216702     +434     

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