build: switch LVGL default logging from info to warn

this hides all LVGL info messages about UI interactions like events,
making the log output more useful during development.

it is still possible to increase verbosity to the original level using
the lvgl_loglevel build flag.

build.zig

@@ -299,10 +299,9 @@ const LVGLLogLevel = enum {
     none,
 
     /// returns default mode based on the compiler optimization flags.
-    /// similar to std.log.default_level.
     fn default(mode: std.builtin.Mode) @This() {
         return switch (mode) {
-            .Debug => .info,
+            .Debug => .warn,
             .ReleaseSafe => .warn,
             .ReleaseFast, .ReleaseSmall => .err,
         };