Fix folderManager NPE issue in WALNode when starting iotdb in a disk-full state

[OneSizeFitsQuorum]

This PR addresses an NPE issue in WALNode creation that occurs when IoTDB starts with a full disk. When the disk is full at startup, the FolderManager initialization in the constructor fails, leaving it null. If disk space is later freed, subsequent WAL node creation attempts fail with NPE because the folderManager is still null.

[Copilot]

Pull request overview

This PR addresses an NPE issue in WALNode creation that occurs when IoTDB starts with a full disk. When the disk is full at startup, the FolderManager initialization in the constructor fails, leaving it null. If disk space is later freed, subsequent WAL node creation attempts fail with NPE because the folderManager is still null.

Key Changes:

• Adds lazy initialization of FolderManager in the createWALNode method to handle recovery after disk space becomes available

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[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 80.00000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 38.87%. Comparing base (f4d628a) to head (cd69d06).

Files with missing lines	Patch %	Lines
...wal/allocation/AbstractNodeAllocationStrategy.java	80.00%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master   #16869      +/-   ##
============================================
- Coverage     38.87%   38.87%   -0.01%     
  Complexity      207      207              
============================================
  Files          5021     5021              
  Lines        333052   333058       +6     
  Branches      42389    42389              
============================================
- Hits         129487   129484       -3     
- Misses       203565   203574       +9     

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