Qualcomm AI Engine Direct - Add rewrite function of observer

[chunit-quic]

• Add function to rewrite observer after prepare_pt2e
• Add corresponding test case

[pytorch-bot]

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[chunit-quic]

Hi @cccclai,

This PR is for the requested functionality to overwrite a quanization parameters after calibration. It can handle shared observer too. Thank you!

[cccclai]

@chunit-quic thanks for putting up the pr. cc: @sxu @billmguo

[cccclai]

Mind sharing a bit more details for the request? I probably miss it

[chunit-quic]

Mind sharing a bit more details for the request? I probably miss it

No problem. :)
We received some feature requests in a mail thread regarding quantization requirements. This particular request is for the following purpose:

The QNN Quantizer should allow users to override quantization parameters for specific tensors, regardless of the data ranges observed during calibration or QAT. This override must respect the transitive closures established by SharedQuantizationSpec.

After a brief discussion your team, we concluded that the rewriting stage should occur after calibration but before conversion. That's essentially the background.