fix(async): improve deadline() validation and performance

[tomas-zijdemans]

• Add NaN input validation (throws TypeError)
• Fix docs to clarify >= MAX_SAFE_INTEGER boundary
• Skip AbortSignal.any() overhead for single-signal cases
• Add test for NaN handling

Benchmarks show ~2.7× faster for the common timeout-only case, ~7× faster when no deadline is needed. The dual-signal path is roughly equivalent.

[codecov]

Codecov Report

❌ Patch coverage is 89.47368% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 94.17%. Comparing base (0ee1ea6) to head (21eed1f).
⚠️ Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
async/deadline.ts	89.47%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6921      +/-   ##
==========================================
- Coverage   94.18%   94.17%   -0.01%     
==========================================
  Files         584      584              
  Lines       43120    43134      +14     
  Branches     6894     6899       +5     
==========================================
+ Hits        40611    40621      +10     
- Misses       2457     2460       +3     
- Partials       52       53       +1     

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[tomas-zijdemans]

I closed this PR, since the NaN check seems overkill and the code got a bit over-engineered. Feel free to merge it if you still like it :D