renderer/OpenGL: use compressed texture formats for images

BPTC is required to be available OpenGL >= 4.2 and our minimum is 4.3 so
this is safe in terms of support. I tested briefly in a VM and didn't
encounter any problems so this should just be a complete win.

(Note: texture data is already automatically compressed on Metal)

src/renderer/OpenGL.zig

@@ -395,7 +395,7 @@ pub inline fn textureOptions(self: OpenGL) Texture.Options {
     _ = self;
     return .{
         .format = .rgba,
-        .internal_format = .srgba,
+        .internal_format = .srgba_compressed,
         .target = .@"2D",
     };
 }

src/renderer/opengl/Texture.zig

@@ -57,7 +57,6 @@ pub fn init(
             opts.internal_format,
             @intCast(width),
             @intCast(height),
-            0,
             opts.format,
             .UnsignedByte,
             if (data) |d| @ptrCast(d.ptr) else null,