Merge PFB and Tx Namespaces

[cmwaters]

Summary

Parent Issue: https://github.com/celestiaorg/celestia-app/issues/2977

This is a proposal to merge the two celestia state machine specific namespaces into a single namespace. This is to be done by modifying the square construction mechanism to populate the TxNamespace with all transaction types including those with PFBs.

Problem Definition

This is meant to address the current emergent problems from when we originally separated into two namespaces:

• A sdk.Tx that has a PFB is not allowed any other sdk.Msg
• PFBs can not use authz
• PFBs are ordered behind non PFBs thus they are dropped first instead of the lowest priority transaction
• The reshuffling messes with nonces making it difficult to have multiple transactions by the same sender in a single block.

Proposal

Create a new square construction protocol (v2 of the go-square repo). That places all transactions in TxNamespace and no longer uses the PFBNamespace.