PCCS crate will panic if used without a tokio runtime

[ameba23]

The PCCS crate uses tokio::spawn which will panic if called outside of a tokio runtime.

We should either:

• Reimlpement dcap_qvl's get_collateral_for_fmspc to use a synchronous http client for fetching if tokio::runtime::Handle::try_current() fails.
• Or clearly document that the PCCS crate will not work without a tokio runtime.

See discussion: #3 (comment)