refactor(jans-cedarling): improve WASM compatibility

[rmarinn]

Is your feature request related to a problem? Please describe.

Cedarling can't compile to WASM because of

1. the usage of std::time.
2. the usage of reqwest::blocking::Client

Describe the solution you'd like

• The chrono crate could be used instead of std::time to fetch the time since it has WASM support.
• Use the reqwest::Client with the tokio runtime to remove the blocking api.

Describe alternatives you've considered

An alternative solution is to write our own interface to the JS Date API.

Additional context
N/A