feat: add support for SharedArrayBuffer in DataViews

[KevinEady]

• Add support for passing Napi::SharedArrayBuffer into Napi::DataView::New() overloads
• Add DataView::Buffer()
• Update docs and tests

[codecov-commenter]

Codecov Report

❌ Patch coverage is 75.00000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 63.54%. Comparing base (fe0c48e) to head (87673ba).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
napi-inl.h	75.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1714      +/-   ##
==========================================
+ Coverage   63.50%   63.54%   +0.03%     
==========================================
  Files           3        3              
  Lines        2047     2049       +2     
  Branches      728      728              
==========================================
+ Hits         1300     1302       +2     
  Misses        162      162              
  Partials      585      585              

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[legendecas]

We can mark this as deprecated and recommend Buffer().

[KevinEady]

I'm actually not so sure about marking this as deprecated anymore. If the add-on author knows for a fact that the DataView will always contain an ArrayBuffer and never a SharedArrayBuffer, it just seems like an extra step for the author to write dataview.Buffer().As<SharedArrayBuffer>() ...

[KevinEady]

We discussed in the 13 March 2026 to update the documentation on ///< Gets the backing array buffer. to say what happens with the As() typechecking like mentioned in the dataview.md document.

[legendecas]

Suggested change

	Napi::Value Buffer() const;
	Napi::Value Buffer() const; ///< Gets the backing ArrayBuffer or SharedArrayBuffer.