Lower unimplemented OSC from warning to debug (#10184)

The "unimplemented OSC command" warning is a frequent source of red
herrings as there are many OSCs that we parse but deliberately do not
implement. It's also a small drag on performance due to the function
call overhead and the overhead of formatting and outputting the message.
This PR lowers the message from warning to debug. Debug logs are
compiled out of release builds so there should be less confusion from
general users who will no longer see the message.

src/terminal/stream.zig

@@ -2108,7 +2108,7 @@ pub fn Stream(comptime Handler: type) type {
                 .conemu_wait_input,
                 .conemu_guimacro,
                 => {
-                    log.warn("unimplemented OSC callback: {}", .{cmd});
+                    log.debug("unimplemented OSC callback: {}", .{cmd});
                 },
 
                 .invalid => {