Update qkeras converter for array and auto po2 scale

[jurevreca12]

This PR updates the QKeras converter to enable it to convert neural networks with tensor scale factors, and with scale factors set to "auto_po2".

Previously the converter added a "Quant" node for every "quantized_bits" function in qkeras. Now it adds an additional "Mul" node after a Quant node. This is because of differences in how QKeras and QONNX handle dequantization.

This additional "Mul" node might be a problem for downstream onnx uses, but can be removed when scale factors are equal to one using a transform.

This PR "follows" after PR: Rounding mode new #134 which introduces additional rounding modes. This is why it contains rounding mode changes for now (since they are not yet merged into main).