Move Blob, BlobTx, and NMTProof, to their own module

[evan-forbes]

We have types such as Blob and BlobTx that were originally defined in here. We might even be able to eventually completely remove them from this repo now that we have removed the Blob type from the block data. Before doing that, we should move them to their own module. Ideally we also move some core types and functions, such as types.Tx and crypto/merkle to their own module as well, but I'm still unsure of the repercussions of that.

This will allow us to create modules here that are importable by other projects that can't import two forks of tendermint without delving into dependency hell. This will be useful specifically for rollkit, who needs to import the shares package. It would also allow for us to modularize the blob and user packages, which would allow for teams to import and sign PFBs without needing to replace their own version of tendermint or the sdk with our forks (note that this would be a bit of a foot gun, since if the core types used by our forks ever deviate from whatever version is being used there will be weird bugs).

blocking celestiaorg/celestia-app#2570