LinearInt8 layer for inference of int8-quantized LLMs and Arm intrinsics

[lrw04]

Please provide feedback on how the patch could be improved.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 89.47368% with 4 lines in your changes missing coverage. Please review.

Project coverage is 89.52%. Comparing base (bcfec1d) to head (68b4b2d).
Report is 288 commits behind head on master.

Files with missing lines	Patch %	Lines
src/layer/linearint8.cpp	89.47%	4 Missing ⚠️

❗ There is a different number of reports uploaded between BASE (bcfec1d) and HEAD (68b4b2d). Click for more details.

HEAD has 28 uploads less than BASE

Flag	BASE (bcfec1d)	HEAD (68b4b2d)
	30	2

Additional details and impacted files

@@             Coverage Diff             @@
##           master    #5007       +/-   ##
===========================================
- Coverage   94.72%   89.52%    -5.20%     
===========================================
  Files         772      303      -469     
  Lines      228777    89191   -139586     
===========================================
- Hits       216705    79848   -136857     
+ Misses      12072     9343     -2729     

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[lrw04]

oh no, it didn't work

[lrw04]

Closing following @nihui's instructions.