sqlite: add serialize() and deserialize() to DatabaseSync

[thisalihassan]

Add serialize() and .deserialize() methods to DatabaseSync, wrapping the sqlite3_serialize and sqlite3_deserialize. These allow extracting an in-memory database as a Uint8Array and loading one back enabling snapshots, cloning, etc..

Implemenation Notes:

serialize() wraps the SQLite allocated buffer directly in a V8 BackingStore to avoid copying the entire database. #ifdef V8_ENABLE_SANDBOX falls back to a copy path since that configuration forbids external backing stores. deserialize() must copy once because SQLite requires sqlite3_malloc64allocated memory.

Wrote test cases with Claude & GPT 5.4

Refs: #62575

[nodejs-github-bot]

Review requested:

• @nodejs/sqlite

[louwers]

Where is this freed?

[thisalihassan]

sqlite3_deserialize() takes ownership of the buffer when passed SQLITE_DESERIALIZE_FREEONCLOSE

sqlite3_deserialize docs:
"If the SQLITE_DESERIALIZE_FREEONCLOSE bit is set in F, then SQLite will invoke sqlite3_free() on the serialization buffer when the database connection closes. If the SQLITE_DESERIALIZE_RESIZEABLE bit is set, then SQLite will try to increase the buffer size using sqlite3_realloc64() if writes on the database cause it to grow larger than M bytes."

[jasnell]

A comment to that effect would be helpful.

[codecov]

Codecov Report

❌ Patch coverage is 75.30864% with 20 lines in your changes missing coverage. Please review.
✅ Project coverage is 89.70%. Comparing base (e419afd) to head (52f29ac).
⚠️ Report is 8 commits behind head on main.

Files with missing lines	Patch %	Lines
src/node_sqlite.cc	75.30%	11 Missing and 9 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #62579      +/-   ##
==========================================
- Coverage   89.71%   89.70%   -0.01%     
==========================================
  Files         695      695              
  Lines      214441   214522      +81     
  Branches    41062    41077      +15     
==========================================
+ Hits       192384   192438      +54     
+ Misses      14123    14122       -1     
- Partials     7934     7962      +28     

Files with missing lines	Coverage Δ
src/node_sqlite.h	80.64% <ø> (ø)
src/node_sqlite.cc	80.68% <75.30%> (-0.14%)	⬇️

... and 40 files with indirect coverage changes

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