fix: prevent PrefixDB from closing underlying DB and copying prefix

[songgaoye]

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PR checklist

• Tests written/updated
• Changelog entry added in .changelog (we use unclog to manage our changelog)

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Note

• PrefixDB behavior: NewPrefixDB now defensively copies prefix (cp(prefix)), and Close() is a no-op to avoid closing the underlying DB.
• Build tooling: Updates tools/Dockerfile to use RocksDB 9.11.2.

^{Written by Cursor Bugbot for commit f6ee7c5. This will update automatically on new commits. Configure here.}

[codecov]

Codecov Report

❌ Patch coverage is 33.33333% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 78.50%. Comparing base (fb4f703) to head (c67e67e).
⚠️ Report is 76 commits behind head on main.

Files with missing lines	Patch %	Lines
prefixdb.go	33.33%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #283      +/-   ##
==========================================
+ Coverage   76.80%   78.50%   +1.69%     
==========================================
  Files          23       23              
  Lines        2048     1698     -350     
==========================================
- Hits         1573     1333     -240     
+ Misses        403      292     -111     
- Partials       72       73       +1     

Files with missing lines	Coverage Δ
prefixdb.go	73.87% <33.33%> (+3.52%)	⬆️

... and 21 files with indirect coverage changes

Files with missing lines	Coverage Δ
prefixdb.go	73.87% <33.33%> (+3.52%)	⬆️

... and 21 files with indirect coverage changes

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