ffi: keep wrapped functions non-constructible

[trivikr]

Fixes: #65183

Use concise method functions for Fast API and shared-buffer wrappers so they preserve the native FFI functions' non-constructible behavior.

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Assisted-by: codex:gpt-5.6-sol

[nodejs-github-bot]

Review requested:

• @nodejs/ffi

[codecov]

Codecov Report

❌ Patch coverage is 47.82609% with 24 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.33%. Comparing base (6fec5e8) to head (edd2a79).
⚠️ Report is 5 commits behind head on main.

Files with missing lines	Patch %	Lines
lib/internal/ffi-shared-buffer.js	33.33%	24 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #65184      +/-   ##
==========================================
+ Coverage   90.32%   90.33%   +0.01%     
==========================================
  Files         760      760              
  Lines      248523   248527       +4     
  Branches    46896    46887       -9     
==========================================
+ Hits       224469   224507      +38     
+ Misses      15465    15459       -6     
+ Partials     8589     8561      -28     

Files with missing lines	Coverage Δ
lib/internal/ffi/fast-api.js	94.80% <100.00%> (+0.02%)	⬆️
lib/internal/ffi-shared-buffer.js	55.57% <33.33%> (+0.16%)	⬆️

... and 29 files with indirect coverage changes

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