OPEN: Fixes for Transformer quantization and Deeploy export

[Scheremo]

This PR fixes smaller issues with the Transformer quantization flow and network export to Deeploy.

Added

• skip_identity_rqs flag for the Integerizer; this flag allows to configure whether to skip Requantshift operators whose source and image epsilon are the same. Default behaviour does not change.

Changes

• OpTreeReplacementPass now doesn't require the quant entry in the meta dict of nodes, but will still copy it if it is available.

Fixed

• ApproximateSoftmaxPass now returns a new instance for every call, rather than sharing the same object.

[Victor-Jung]

Two questions out of curiosity:

• Why was the quant field of the meta dict required to apply the replacement pass?
• Why would you keep an RQS that is performing an identity operation?

Otherwise LGTM.

[Scheremo]

Two questions out of curiosity:

* Why was the `quant` field of the `meta` dict required to apply the replacement pass?

* Why would you keep an RQS that is performing an identity operation?

Otherwise LGTM.

The deal with the quant key / meta field in the OpTreeReplacementPass is that if this information is annotated prior to OpTreeReplacement, you'd like to have it afterwards as well; the code added just makes sure it also works if the information was not annotated before hand (since it's not really required).

Keeping an RQS preserves semantic information; in principle there could be an identity RQS after a convolution which might get removed; to Deeploy, this pattern would look like an unquantized convolution. If we decide we don't want to do identity RQS operations in deployment, we remove them during lowering in Deeploy.

[Victor-Jung]

Thanks for the details. I have no objection. Good to merge!