lib: use Object.freeze to avoid defensive cloning in SourceMap

[watilde]

No description provided.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.68%. Comparing base (58a8e1d) to head (73ffd8a).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #62830      +/-   ##
==========================================
- Coverage   89.69%   89.68%   -0.01%     
==========================================
  Files         706      706              
  Lines      218222   218220       -2     
  Branches    41768    41767       -1     
==========================================
- Hits       195731   195713      -18     
- Misses      14411    14414       +3     
- Partials     8080     8093      +13     

Files with missing lines	Coverage Δ
lib/internal/source_map/source_map.js	99.48% <100.00%> (+0.25%)	⬆️

... and 23 files with indirect coverage changes

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