Add HomeStore superblock decoder and validator

[xiaoxichen]

This tool decodes and validates HomeStore superblock structures from disk dumps.
It checks bitmap consistency, CRC integrity, and VDev allocation.

Usage:
# Quick validation summary
python3 decode_superblock.py <disk_dump>

# Detailed verbose output
python3 decode_superblock.py <disk_dump> --verbose

# Inspect specific chunk
python3 decode_superblock.py <disk_dump> chunk 512

# Inspect specific vdev
python3 decode_superblock.py <disk_dump> vdev 0
python3 decode_superblock.py <disk_dump> vdev meta

What it validates:

• First block magic number and metadata
• Bitmap vs chunk array consistency
• Chunk CRC checksums (detects corruption)
• VDev allocation and utilization
• Orphan chunks (corrupted vdev_id)

Exit codes:
0 = All validations passed 1 = Issues detected (CRC errors, bitmap inconsistencies, orphans)

Common issues detected:

• CRC mismatch: Chunk data corrupted on disk
• Bitmap inconsistency: Bitmap/chunk allocation out of sync
• Orphan chunks: Chunks with invalid/corrupted vdev_id

[xiaoxichen]

This is a BORING code written by AI , lets focus more on functional

☆SDDZ☆xiaoxchen@QFHYQ56F7P HomeStore % python3 tools/superblock_checker.py ./sm1.data.32m

HomeStore Superblock Summary
================================================================================
Product: HomeStore4x v5
System UUID: 84ba0a2b-b9f4-459f-8a69-6d575eba4ac1
Formatting: Complete
Device: pdev_id=1, size=111.76 TB, data_offset=1.75 GB

VDevs (4 total):
  [0] META_VDEV    'meta    '   5721.96 GB  1,430 chunks    100% util  ✓
  [1] LOGDEV_VDEV  'LogDev  '      2.88 GB     92 chunks    100% util  ✓
  [2] INDEX_VDEV   'index   '   5721.96 GB  1,431 chunks    100% util  ✓
  [3] DATA_VDEV    'blkdata '  90406.00 GB  45,203 chunks    100% util  ✓

Chunks:
  Total allocated: 48,157 / 65,536 (73.5%)
  Valid checksums: 48,156 (100.0%)
  Invalid:         1

Issues:
  ✗ 1 chunks with CRC errors:
  ✗ 1 orphan chunks (corrupted vdev_id):
    Slot 512 (vdev_id=1547590718 INVALID): CRC error: stored=0x0000 calc=0x5d31

Status: ⚠ ISSUES DETECTED

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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 48.22%. Comparing base (1a0cef8) to head (014a977).
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Additional details and impacted files

@@            Coverage Diff             @@
##           master     #873      +/-   ##
==========================================
- Coverage   56.51%   48.22%   -8.30%     
==========================================
  Files         108      110       +2     
  Lines       10300    12894    +2594     
  Branches     1402     6198    +4796     
==========================================
+ Hits         5821     6218     +397     
+ Misses       3894     2561    -1333     
- Partials      585     4115    +3530     

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