command/player, SongPrint: use AudioFormatFormatter()

libfmt version 10 apparently doesn't know how to format a
`StringBuffer`, failing the MPD build.  Since we have a formatter
specialization for `AudioFormat`, let's use that - it's better and
easier to use.

Closes #1807

src/SongPrint.cxx

@@ -8,6 +8,7 @@
 #include "TagPrint.hxx"
 #include "client/Response.hxx"
 #include "fs/Traits.hxx"
+#include "lib/fmt/AudioFormatFormatter.hxx"
 #include "time/ChronoUtil.hxx"
 #include "util/StringBuffer.hxx"
 #include "util/UriUtil.hxx"
@@ -77,7 +78,7 @@ song_print_info(Response &r, const LightSong &song, bool base) noexcept
 		time_print(r, "Last-Modified", song.mtime);
 
 	if (song.audio_format.IsDefined())
-		r.Fmt(FMT_STRING("Format: {}\n"), ToString(song.audio_format));
+		r.Fmt(FMT_STRING("Format: {}\n"), song.audio_format);
 
 	tag_print_values(r, song.tag);
 
@@ -100,7 +101,7 @@ song_print_info(Response &r, const DetachedSong &song, bool base) noexcept
 		time_print(r, "Last-Modified", song.GetLastModified());
 
 	if (const auto &f = song.GetAudioFormat(); f.IsDefined())
-		r.Fmt(FMT_STRING("Format: {}\n"), ToString(f));
+		r.Fmt(FMT_STRING("Format: {}\n"), f);
 
 	tag_print_values(r, song.GetTag());
 

src/command/PlayerCommands.cxx

@@ -13,6 +13,7 @@
 #include "Partition.hxx"
 #include "Instance.hxx"
 #include "IdleFlags.hxx"
+#include "lib/fmt/AudioFormatFormatter.hxx"
 #include "util/StringBuffer.hxx"
 #include "util/ScopeExit.hxx"
 #include "util/Exception.hxx"
@@ -170,7 +171,7 @@ handle_status(Client &client, [[maybe_unused]] Request args, Response &r)
 
 		if (player_status.audio_format.IsDefined())
 			r.Fmt(FMT_STRING(COMMAND_STATUS_AUDIO ": {}\n"),
-			      ToString(player_status.audio_format));
+			      player_status.audio_format);
 	}
 
 #ifdef ENABLE_DATABASE