refactor: Relax runtime checks in MergedRegistry

[amaury1093]

Previous PR #37 introduced 2 runtime checks:

• require that import paths are correct
• require that file descriptors match

This PR still performs those checks, but logs warnings instead of throwing error.

---

When calling proto.MergedRegistry, we would have the following warning:

Got 2 file descriptor import path errors and 14 file descriptor mismatches. Run `proto.DebugFileDescriptorsMismatch` to debug them.

This is probably hard to debug, so I added a new helper function DebugFileDescriptorsMismatch, which errors with:

-- snip --
Got 2 file descriptor import path errors:
	file name internal/errors.proto does not start with expected grpc/gateway/runtime/; please make sure your folder structure matches the proto files fully-qualified names
	file name grpc/binlog/v1/binarylog.proto does not start with expected grpc/binarylog/v1/; please make sure your folder structure matches the proto files fully-qualified names
Got 14 file descriptor mismatches. Make sure gogoproto and protoregistry use the same .proto files. '-' lines are from protoregistry, '+' lines from gogo's registry.

	Mismatch in cosmos/msg/v1/msg.proto:
  (*descriptorpb.FileDescriptorProto)(Inverse(protocmp.Transform, protocmp.Message{
  	... // 2 identical entries
  	"extension": []protocmp.Message{{"@type": s"google.protobuf.FieldDescriptorProto", "extendee": string(".google.protobuf.ServiceOptions"), "json_name": string("service"), "label": s"LABEL_OPTIONAL", ...}, {"@type": s"google.protobuf.FieldDescriptorProto", "extendee": string(".google.protobuf.MessageOptions"), "json_name": string("signer"), "label": s"LABEL_REPEATED", ...}},
  	"name":      string("cosmos/msg/v1/msg.proto"),
  	"options": protocmp.Message{
+ 		"63017":            protoreflect.RawFields{0xc8, 0xe2, 0x1e, 0x01},
+ 		"63018":            protoreflect.RawFields{0xd0, 0xe2, 0x1e, 0x01},
+ 		"63020":            protoreflect.RawFields{0xe0, 0xe2, 0x1e, 0x01},
+ 		"63026":            protoreflect.RawFields{0x90, 0xe3, 0x1e, 0x00},
+ 		"63034":            protoreflect.RawFields{0xd0, 0xe3, 0x1e, 0x00},
+ 		"63035":            protoreflect.RawFields{0xd8, 0xe3, 0x1e, 0x00},
  		"@type":            s"google.protobuf.FileOptions",
- 		"csharp_namespace": string("Cosmos.Msg.V1"),
  		"go_package": strings.Join({
- 			"cosmossdk.io/api/cosmos/msg/v1;msgv1",
+ 			"github.com/cosmos/cosmos-sdk/types/msgservice",
  		}, ""),
- 		"java_multiple_files":    bool(true),
- 		"java_outer_classname":   string("MsgProto"),
- 		"java_package":           string("com.cosmos.msg.v1"),
- 		"objc_class_prefix":      string("CMX"),
- 		"php_metadata_namespace": string(`Cosmos\Msg\V1\GPBMetadata`),
- 		"php_namespace":          string(`Cosmos\Msg\V1`),
- 		"ruby_package":           string("Cosmos::Msg::V1"),
  	},
  	"package": string("cosmos.msg.v1"),
  	"syntax":  string("proto3"),
  }))
-- snip --