Use once_cell instead of lazy_static

This seems to be generally considered the preferred, idiomatic solution
now. This is in the standard library behind a feature flag (apparently
now called `std::sync::LazyLock`).

examples/todos/Cargo.toml

@@ -7,9 +7,9 @@ publish = false
 
 [dependencies]
 iced = { path = "../..", features = ["async-std", "debug"] }
+once_cell = "1.15.0"
 serde = { version = "1.0", features = ["derive"] }
 serde_json = "1.0"
-lazy_static = "1.4"
 
 [target.'cfg(not(target_arch = "wasm32"))'.dependencies]
 async-std = "1.0"