async fn select_n(
rng: &mut (impl RngCore + CryptoRng),
rpc: &impl ProvidesDecoys,
block_number: usize,
output_being_spent: &WalletOutput,
ring_len: u8,
fingerprintable_deterministic: bool,
) -> Result<Vec<(u64, [Point; 2])>, TransactionsError>