Fallback to flat when no oxr runtime is found (#51)

* basics done? now to the fun part: changing the ENTIRE lib to work with xr and non xr

* updated stuff and renamed file

* actually add the renamed file into git lol :3

* made lib fallback to flat when no runtime is found but can't compile with default settings under those circumstances

Cargo.toml

@@ -18,6 +18,7 @@ members = ["examples/android", "examples/demo"]
 anyhow = "1.0.75"
 ash = "0.37.3"
 bevy = "0.12"
+futures-lite = "2.1.0"
 mint = "0.5.9"
 wgpu = "0.17.1"
 wgpu-core = { version = "0.17.1", features = ["vulkan"] }