bytes, utils: include fmt/iostream.h and iostream when appropriate

in seastar e96932b05f394b27cd0101e24f0584736795b50f, we stopped
including unused `fmt/ostream.h`. this helped to reduce the header
dependency. but this also broke the build of scylladb, as we rely
on the `fmt/ostream.h` indirectly included by seastar's header project.

in this change, we include `fmt/iostream.h` and `iostream` explictly
when we are using the declarations in them. this enables us to

- bump up the seastar submodule
- potentially reduce the header dependency as we will be able to
  include seastar/core/format.hh instead of a more bloated
  seastar/core/print.hh after bumping up seastar submodule

Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>

Closes scylladb/scylladb#21494

bytes.cc

@@ -7,6 +7,7 @@
  */
 
 #include "bytes.hh"
+#include <fmt/ostream.h>
 #include <seastar/core/print.hh>
 
 static inline int8_t hex_to_int(unsigned char c) {

utils/estimated_histogram.hh

@@ -15,6 +15,7 @@
 #include <algorithm>
 #include <vector>
 #include <chrono>
+#include <fmt/ostream.h>
 #include <seastar/core/metrics_types.hh>
 #include <seastar/core/print.hh>
 #include "seastarx.hh"

utils/rjson.hh

@@ -26,6 +26,7 @@
  * or calling Size() on a non-array value.
  */
 
+#include <iostream>
 #include <string>
 #include <string_view>
 #include <type_traits>

utils/uuid.cc

@@ -13,6 +13,7 @@
 #include <boost/iterator/function_input_iterator.hpp>
 #include <boost/algorithm/string.hpp>
 #include <string>
+#include <fmt/ostream.h>
 #include <seastar/core/sstring.hh>
 #include "marshal_exception.hh"