Port attributes

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Adds port attributes of the form

#[attrib]
port: ['G, 'G+1] 32,
...

Also can technically be used within bundle definitions like

bundle #[attrib] bun[3]: for<i> ['G + i, 'G+i+1] 32;

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I should add a test case for this but right now there are no implemented attributes...

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@rachitnigam if there are no problems here I will merge this and start using it in the scheduling pass. My one question remaining is whether it is a good idea to store an Attributes in every port, considering we are trying to lower the size of the actual control elements. ALternatively we would have to create an IndexStore but I am not sure how reasonable that is.

[rachitnigam]

There is a way to store information associated with a PortIdx that is not a port itself right? Something like a secondary context?