message: [codec] remove uses of fmt::format, move to absl::StrCat
  Removes the dependency on `fmt::format` in H1 codec. Eliminates the use of `fmt::format` to format HTTP requests. Instead uses `absl::StrCat`, which can handle hex values with `absl::Hex`.
diff: #include "envoy/network/connection.h"
  #include "common/common/enum_to_int.h"
  -#include "common/common/fmt.h"
  #include "common/common/stack_array.h"
  #include "common/common/utility.h"
  #include "common/http/exception.h"
  @@ -171,7 +170,7 @@ void StreamEncoderImpl::encodeData(Buffer::Instance& data, bool end_stream) {
  // actually write the zero length buffer out.
  if (data.length() > 0) {
  if (chunk_encoding_) {
  - connection_.buffer().add(fmt::format("{:x}\r\n", data.length()));
  + connection_.buffer().add(absl::StrCat(absl::Hex(data.length()), CRLF));
  }
  connection_.buffer().move(data);
  @@ -733,8 +732,8 @@ void ServerConnectionImpl::sendProtocolError() {
  // to look more like HTTP/2 to higher layers.
  if (!active_request_ || !active_request_->response_encoder_.startedResponse()) {
  Buffer::OwnedImpl bad_request_response(
  - fmt::format("HTTP/1.1 {} {}\r\ncontent-length: 0\r\nconnection: close\r\n\r\n",
  - std::to_string(enumToInt(error_code_)), CodeUtility::toString(error_code_)));
  + absl::StrCat("HTTP/1.1 ", error_code_, " ", CodeUtility::toString(error_code_),
  + "\r\ncontent-length: 0\r\nconnection: close\r\n\r\n"));
  connection_.write(bad_request_response, false);
  }
  