ompose_extrinsic_offline fails for payloads that don't implement the copy trait

[brenzi]

if the call enum contains a value which doesn't implement copy trait, rustc complains:

error[E0382]: use of moved value: `witnesses`
   --> src/lib.rs:246:87
    |
241 |             let witnesses = witnesses.expect("witnesses are specified");
    |                 --------- move occurs because `witnesses` has type `std::vec::Vec<encointer_node_runtime::encointer_ceremonies::Witness<sr_primitives::AnySignature, substrate_primitives::sr25519::Public>>`, which does not implement the `Copy` trait
...
246 |                 Call::EncointerCeremonies(EncointerCeremoniesCall::register_witnesses(witnesses)),
    |                                                                                       ^^^^^^^^^ value moved here, in previous iteration of loop

The error message is misleading, because there is no loop: due to: rust-lang/rust/issues/46099