Upgrade to mnn 3.0 as well as lot of minor bug fixes

[uttarayan21]

• feat: Update to mnn 3.0.0
• feat: Emit tracing events from mnn
• feat: Apply the patch at compile time with diffy
• feat: rename benchmarks
• feat(tracing): Don't use diffy::patch since that's not working properly
• feat: Don't try to patch MNNDefine with the HalideRuntime patch
• fix(mnn-sys): Fix buildscript typo MNNDefine.hpp -> MNNDefine.h
• broken(coreml): Gatherv2 support in progress
• feat: Added test cases to ensure outputs for multiple backends are same
• feat: Added testing tool
• feat: Added completions
• feat: Added benchmark result generator and checker
• feat: Added nix support for building bencher
• fix: Fixed issue with models not creating cpu tensor using gpu backend
• feat: Use the average of 5 inference runs
• fix: Fix the issue with debugging invalid filling of tensors

[codecov]

Codecov Report

Attention: Patch coverage is 47.04641% with 251 lines in your changes missing coverage. Please review.

Project coverage is 38.24%. Comparing base (a3c20e0) to head (e337d71).
Report is 23 commits behind head on master.

Files with missing lines	Patch %	Lines
src/tensor/raw.rs	11.39%	70 Missing ⚠️
src/schedule.rs	4.91%	58 Missing ⚠️
src/backend.rs	56.38%	41 Missing ⚠️
mnn-sys/src/tracing.rs	72.58%	34 Missing ⚠️
src/tensor/list.rs	72.09%	24 Missing ⚠️
src/interpreter.rs	15.38%	11 Missing ⚠️
src/tensor.rs	27.27%	8 Missing ⚠️
src/error.rs	16.66%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master       #9      +/-   ##
==========================================
+ Coverage   37.53%   38.24%   +0.70%     
==========================================
  Files           9       12       +3     
  Lines        1252     1820     +568     
==========================================
+ Hits          470      696     +226     
- Misses        782     1124     +342     

Flag	Coverage Δ
unittests	38.24% <47.04%> (+0.70%)	⬆️

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