Add ncnn backend

[sunnycase]

• Softmax
• Unary

[github-actions]

Test Results

6 120 tests  +183   6 120 ✅ +183   7m 36s ⏱️ -43s
    6 suites ±  0       0 💤 ±  0 
    6 files   ±  0       0 ❌ ±  0 

Results for commit 782f4c0. ± Comparison against base commit 2498b1b.

♻️ This comment has been updated with latest results.

[codecov]

Codecov Report

Attention: Patch coverage is 75.49407% with 62 lines in your changes missing coverage. Please review.

Project coverage is 73.21%. Comparing base (2498b1b) to head (724b20e).
Report is 17 commits behind head on dev/3.0.

❗ Current head 724b20e differs from pull request most recent head fa74f42

Please upload reports for the commit fa74f42 to get more accurate results.

Files	Patch %	Lines
.../Nncase.Modules.Ncnn/Evaluator/Ncnn/NcnnSoftmax.cs	12.50%	21 Missing ⚠️
...ncase.Modules.Ncnn/Passes/Rules/Ncnn/LowerUnary.cs	0.00%	13 Missing and 1 partial ⚠️
src/Nncase.Core/Runtime/Ncnn/ParamDict.cs	47.61%	6 Missing and 5 partials ⚠️
modules/Nncase.Modules.Ncnn/IR/Ncnn/NcnnUnary.cs	0.00%	3 Missing ⚠️
...e.Modules.Ncnn/CodeGen/Ncnn/NcnnFunctionBuilder.cs	92.85%	2 Missing ⚠️
....Modules.Ncnn/CodeGen/Ncnn/NcnnLinkableFunction.cs	90.00%	2 Missing ⚠️
src/Nncase.Core/Runtime/Ncnn/NcnnLayer.cs	91.30%	2 Missing ⚠️
...case.Modules.Ncnn/CodeGen/Ncnn/NcnnLinkedModule.cs	91.66%	0 Missing and 1 partial ⚠️
...ase.Modules.Ncnn/CodeGen/Ncnn/NcnnModuleBuilder.cs	66.66%	1 Missing ⚠️
modules/Nncase.Modules.Ncnn/IR/Ncnn/Functional.cs	50.00%	1 Missing ⚠️
... and 4 more

Additional details and impacted files

@@             Coverage Diff             @@
##           dev/3.0    #1107      +/-   ##
===========================================
- Coverage    73.26%   73.21%   -0.05%     
===========================================
  Files          706      723      +17     
  Lines        25960    26025      +65     
  Branches      4229     4233       +4     
===========================================
+ Hits         19019    19055      +36     
- Misses        6294     6323      +29     
  Partials       647      647              

Flag	Coverage Δ
integration	39.60% <75.09%> (+0.28%)	⬆️
unit	64.54% <11.85%> (-0.16%)	⬇️

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