Refactor: rename usage counter

[szszszsz]

Current usage counter for the credentials is named timestamp, which is misleading. Should be use_counter or anything resembling.

fido-authenticator/src/state.rs

Lines 351 to 355 in 4022d6c

	pub fn timestamp<T: TrussedClient>(&mut self, trussed: &mut T) -> Result<u32> {
	let now = self.timestamp;
	self.timestamp += 1;
	self.save(trussed)?;
	Ok(now)