refactor(diagnostics) move proto to internal pb package

https://docs.google.com/document/d/1e8kOo3r51b2BWtTs_1uADIA5djfXhPT36s6eHVRIvaU/edit
refactor(exchange/bitswap) move proto to internal pb package
refactor(net/service) move proto to internal pb package
refactor(merkledag) move proto to internal pb package

https://docs.google.com/document/d/1e8kOo3r51b2BWtTs_1uADIA5djfXhPT36s6eHVRIvaU/edit
fix(fuse/ipns) use pb package
fix(fuse) named/aliased imports
fix(fuse/ipns) use aliased/named imports
fix(fuse) import protos from unixfs/pb package
fix(diags/pb) rename package -> pb
fix(net/service/pb) rename package -> pb
fix(merkledag/pb) rename package -> pb
fix(crypto/pb) rename package -> pb
fix(namesys/pb) rename package -> pb
fix(spipe) rename package -> pb
fix(net/mux/pb) rename package -> pb
fix(unixfs/pb) rename package -> pb
fix(crypto/spipe/pb) rename proto file -> spipe.proto