PCCS crate will panic if used without a tokio runtime

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: https://github.com/flashbots/attested-tls/pull/3#discussion_r2974715361