Change packet key to support efficient iteration in v2

[colin-axner]

Summary

Change packet keys to use big endian encodings on the sequence to support efficient iteration

Problem Definition

Packet keys which have sequences which are lexographically ordered are not efficient to iterate and cause issues later on which are hard to workaround. See #5413 for example. This will also be problematic if we tried to create a pruning solution as we cannot easily iterate. We would need to do individual deletions or queries to the store.

Proposal

The "Eureka" version of IBC introduces a V2 to the packet commitment structure. Given that we are changing how we are committing to packets, we might as well change how we are storing these packet commitments, so that we can future proof the protocol and make future features, like pruning, much easier to implement

I propose changing the packet key structure to be:

clients/<client-ID/sequences/<big-endian-encoded-sequence>

Currently we use:
ports/<port-ID>/channels/<channel-id>/sequences/<sequence>

I think the port ID should be moved to the commitment value (this would be in-line with multi-packetdata) and I think we should be more explicit in the future approach that we are using clientIDs not channelIDs, but I haven't given these additional points much thought, so I am happy to exclude them. The big endian encoding of the sequence should definitely be done

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For Admin Use

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• Appropriate labels applied
• Appropriate contributors tagged/assigned

[crodriguezvega]

Note: if we decide to use the proposed new path key we should also document this in the specs.

[DimitrisJim]

#5752 umbrella issue on some level

[AdityaSripal]

This has been changed in the spec: cosmos/ibc#1144

[DimitrisJim]

sequence in keys formatted using Big Endian in #7378