[OMNIML-2244] enable fp8 and int8 ONNX export

[ajrasane]

What does this PR do?

Type of change:
Example update

Overview:

• Support ONNX export for fp8 and int8 precisions
• Added utility functions to check for fp8 and int8 quantization (will be used in ONNXExporter)
• Fixed a bug in evaluation API for high batch sizes
• Added function to replace zeros from scales to smallest positive value in fp16

Usage

python torch_quant_to_onnx.py \
    --quantize_mode fp8/int8 \
    --onnx_save_path <onnx_path>  

Testing

Validated the accuracy and latency of int8 and fp8 models:

Metric	INT8	FP8
Top1 Accuracy	84.584%	85.062%
Top5 Accuracy	97.3%	97.534%
Inference Latency	8.4825 ms	8.15096 ms

Before your PR is "Ready for review"

• Make sure you read and follow Contributor guidelines and your commits are signed.
• Is this change backward compatible?: Yes
• Did you write any new necessary tests?: No
• Did you add or update any necessary documentation?: Yes
• Did you update Changelog?: No

[cjluo-nv]

do we still consider mixed precision here?

[ajrasane]

This MR targets models with only FP8 and INT8 quantization. For mixed precision, I will update the following function with this utility function.

[codecov]

Codecov Report

❌ Patch coverage is 13.04348% with 20 lines in your changes missing coverage. Please review.
✅ Project coverage is 74.39%. Comparing base (1aaa77d) to head (6d35c45).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
modelopt/onnx/quantization/qdq_utils.py	8.33%	11 Missing ⚠️
modelopt/torch/_deploy/utils/torch_onnx.py	18.18%	9 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #594      +/-   ##
==========================================
- Coverage   74.45%   74.39%   -0.07%     
==========================================
  Files         182      182              
  Lines       18250    18273      +23     
==========================================
+ Hits        13588    13594       +6     
- Misses       4662     4679      +17     

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