The `MilliSecondsSinceUnixEpoch::to_system_time()` method returns the
`SystemTime` type from the standard library.
The `std::time::SystemTime::elapsed()` method sadly panics under WASM.
Instead of returning the `SystemTime` from the standard library we're
now returning a drop-in replacement of this type coming from the web-time
crate.
ccd3b81557