ffi: preserve uint8 semantics for bool fast calls

[trivikr]

Fixes: #64526

node:ffi documents bool as an 8-bit unsigned integer, but the Fast
API path mapped it to V8's Boolean type. As a result, behavior changed
after JIT optimization:

• return values changed from numbers to JavaScript Booleans;
• true and false became accepted as arguments.

This change normalizes bool to the existing kUint8 Fast FFI type and
removes the now-unused kBool type. The regression test forces V8
optimization and verifies that numeric return values and argument
validation remain consistent.

---

Assisted-by: openai:gpt-5.6-sol

[nodejs-github-bot]

Review requested:

• @nodejs/ffi
• @nodejs/tsc

[codecov]

Codecov Report

❌ Patch coverage is 0% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 90.25%. Comparing base (f2ba101) to head (ae0ca8d).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/ffi/fast.cc	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #64527      +/-   ##
==========================================
- Coverage   92.01%   90.25%   -1.77%     
==========================================
  Files         379      739     +360     
  Lines      170129   241649   +71520     
  Branches    26090    45542   +19452     
==========================================
+ Hits       156544   218098   +61554     
- Misses      13293    15093    +1800     
- Partials      292     8458    +8166     

Files with missing lines	Coverage Δ
src/ffi/fast.h	100.00% <ø> (ø)
src/ffi/platforms/arm64.cc	86.90% <ø> (ø)
src/ffi/fast.cc	66.66% <0.00%> (ø)

... and 481 files with indirect coverage changes

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[ShogunPanda]

Can you please run comparison benchmarks to make sure nothing regresses?

[trivikr]

Can you please run comparison benchmarks to make sure nothing regresses?

Did you mean benchmark-node-micro-benchmarks?

[ShogunPanda]

No, I meant something like:

./node-new --no-warnings --experimental-ffi benchmark/compare.js --old ./node-old --new ./node-new --runs 30 --no-progress ffi > compare.csv

And then

npx node-benchmark-compare compare.csv

Note that you need to compile Node twice, once before and once after your changes.

[trivikr]

Benchmark output for add-u8 which this PR touches

                         confidence improvement accuracy (*)   (**)  (***)
ffi/add-u8.js n=10000000                 0.75 %       ±1.47% ±1.95% ±2.54%

[ShogunPanda]

Do you mind posting the entire benchmark? I just want to make sure there are not regressions elsewhere.