mach: introduce cross platform Timer abstraction

This Timer uses std.time.Timer as backing timer in native platforms, and
will use custom timers for special platforms (wasm, android?, ios?).

Unlike std.time.Timer, its primary API is focused on floats. Also meant
to provides some convenient functions alongside base ones.

Follows std.time.Timer API, but methods by default return f32 i.e
non-precise variant with precise variants available returning u64.

src/Engine.zig

@@ -5,6 +5,7 @@ const gpu = @import("gpu");
 const App = @import("app");
 const structs = @import("structs.zig");
 const enums = @import("enums.zig");
+const Timer = @import("Timer.zig");
 
 const Engine = @This();
 
@@ -23,9 +24,9 @@ options: structs.Options,
 /// For example, if you are animating a cube which should rotate 360 degrees every second,
 /// instead of writing (360.0 / 60.0) and assuming the frame rate is 60hz, write
 /// (360.0 * engine.delta_time)
-delta_time: f64 = 0,
+delta_time: f32 = 0,
 delta_time_ns: u64 = 0,
-timer: std.time.Timer,
+timer: Timer,
 
 pub const Core = struct {
     internal: GetCoreInternalType(),
@@ -64,7 +65,7 @@ pub fn init(allocator: std.mem.Allocator, options: structs.Options) !Engine {
     var engine = Engine{
         .allocator = allocator,
         .options = options,
-        .timer = try std.time.Timer.start(),
+        .timer = try Timer.start(),
         .core = undefined,
         .gpu_driver = undefined,
     };