renderer/size: move PaddingBalance enum out of Config

Previously WindowPaddingBalance was defined inside Config.zig, which
meant tests for renderer sizing had to pull in the full config
dependency. Move the enum into renderer/size.zig as PaddingBalance
and re-export it from Config so the public API is unchanged. This
lets size.zig tests run without depending on Config.

src/config/Config.zig

@@ -39,6 +39,7 @@ pub const Path = @import("path.zig").Path;
 pub const RepeatablePath = @import("path.zig").RepeatablePath;
 const ClipboardCodepointMap = @import("ClipboardCodepointMap.zig");
 const KeyRemapSet = @import("../input/key_mods.zig").RemapSet;
+pub const WindowPaddingBalance = @import("../renderer/size.zig").PaddingBalance;
 const string = @import("string.zig");
 
 // We do this instead of importing all of terminal/main.zig to
@@ -5245,12 +5246,6 @@ pub const Fullscreen = enum(c_int) {
     @"non-native-padded-notch",
 };
 
-pub const WindowPaddingBalance = enum {
-    false,
-    true,
-    equal,
-};
-
 pub const WindowPaddingColor = enum {
     background,
     extend,