`get_sigs`'s params should contain a `txid` not an `id` field.

[darosior]

Caught while implementing the coordinator cache in Python...

https://github.com/revault/practical-revault/blob/master/messages.md#request-3

revault_net/src/message.rs

Lines 261 to 266 in f84f411

	/// Sent by a wallet to retrieve all signatures for a specific transaction
	#[derive(Debug, PartialEq, Clone, Serialize, Deserialize)]
	pub struct GetSigs {
	/// Transaction id
	pub id: Txid,
	}