change(serverv2/comet): use codec to parse gRPC requests

[testinginprod]

We need to pass codec to comet to properly decode gRPC requests.

Originally posted by @tac0turtle in #21038 (comment)

[psiphi5]

I had a look at the PR that had the v2/server change (#21038) and wanted to ask if this would require re-adding the GRPCQueryDecoders field the App struct? Also why is it better to decode via codec, since both ways return a gogoproto.Message?

[psiphi5]

Hi @tac0turtle I had a look at gogoproto and wanted to check if using a codec would mean a change like:

diff --git a/server/v2/cometbft/abci.go b/server/v2/cometbft/abci.go
index b7a300b05f..c105a4f57b 100644
--- a/server/v2/cometbft/abci.go
+++ b/server/v2/cometbft/abci.go
@@ -10,6 +10,7 @@ import (
        abci "github.com/cometbft/cometbft/abci/types"
        abciproto "github.com/cometbft/cometbft/api/cometbft/abci/v1"
        gogoproto "github.com/cosmos/gogoproto/proto"
+       gogocodec "github.com/cosmos/gogoproto/codec"

        coreappmgr "cosmossdk.io/core/app"
        "cosmossdk.io/core/comet"
@@ -192,7 +193,7 @@ func (c *Consensus[T]) Query(ctx context.Context, req *abciproto.QueryRequest) (
        makeGRPCRequest, isGRPC := c.grpcMethodsMap[req.Path]
        if isGRPC {
                protoRequest := makeGRPCRequest()
-               err = gogoproto.Unmarshal(req.Data, protoRequest) // TODO: use codec
+               err = gogocodec.New(len(req.Data)).Unmarshal(req.Data, protoRequest)
                if err != nil {
                        return nil, fmt.Errorf("unable to decode gRPC request with path %s from ABCI.Query: %w", req.Path, err)
                }

[tac0turtle]

@testinginprod is this still needed?