refactor: update collateral handling

- Simplify collateral handling by removing unnecessary references and matches.
- Add `collateral` field to `QuoteVerificationResult` for improved data clarity.

Signed-off-by: Harald Hoyer <harald@matterlabs.dev>

bin/vault-admin/src/main.rs

@@ -21,7 +21,7 @@ use teepot::{
     server::signatures::verify_sig,
     sgx::sign::Signature,
 };
-use tracing::{error, info, level_filters::LevelFilter};
+use tracing::{error, level_filters::LevelFilter};
 
 #[derive(Args, Debug)]
 struct SendArgs {