src: cut small costs in node::MakeCallback

[nigrosimone]

After #66316, node::MakeCallback still does some work that the common case does not need:

• it enters the Environment's context also when it is already the entered and current one
• it sets the async context frame also when it does not change (usually undefined before and after)
• push_async_context() takes the resource variant by value
• the native resource stack uses resize() where push_back() and pop_back() are enough

Each one is 1-5 ns, together about 10-14 ns per call. type=Call does not use this code. benchmark/compare.js, 30 runs, Linux x64:

                                                    confidence improvement accuracy (*)   (**)  (***)
napi/make_callback n=1000000 type='AsyncResource'           ***      8.76 %  ±3.98% ±5.30% ±6.90%
napi/make_callback n=1000000 type='Call'                            -3.08 %  ±5.30% ±7.06% ±9.19%
napi/make_callback n=1000000 type='MakeCallback'             **      7.92 %  ±5.71% ±7.60% ±9.90%
napi/make_callback n=10000000 type='AsyncResource'            *      5.20 %  ±4.02% ±5.35% ±6.96%
napi/make_callback n=10000000 type='Call'                           -0.04 %  ±5.44% ±7.24% ±9.42%
napi/make_callback n=10000000 type='MakeCallback'           ***     11.15 %  ±3.05% ±4.06% ±5.28%

Refs: nodejs/performance#24

Disclosure: I used Opus 5.5 (Max) as coding assistant

[codecov]

Codecov Report

❌ Patch coverage is 84.21053% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.37%. Comparing base (1f26576) to head (4667f95).

Files with missing lines	Patch %	Lines
src/api/callback.cc	70.00%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #66395      +/-   ##
==========================================
+ Coverage   90.35%   90.37%   +0.02%     
==========================================
  Files         792      792              
  Lines      275500   275515      +15     
  Branches    52791    52808      +17     
==========================================
+ Hits       248932   249003      +71     
+ Misses      16992    16931      -61     
- Partials     9576     9581       +5     

Files with missing lines	Coverage Δ
src/env.cc	82.24% <100.00%> (+0.01%)	⬆️
src/env.h	97.33% <ø> (ø)
src/api/callback.cc	82.64% <70.00%> (-0.77%)	⬇️

... and 29 files with indirect coverage changes

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