Fill BlindingFactor with zeros on Drop (#2847)

* Implement simple zeroing of BlindingFactor in Drop

* rustfmt

* Make Debug implementation for BlindingFactor empty

* Implement BlindingFactor zeroing unit test

* mnemonic.rs: fix deprecated warning in test_bip39_random test

* Use zeroize crate to clear BlindingFactor

* Fix comment and implement dummy Debug trait for BlindingFactor

* Fix formatter

pool/src/pool.rs

@@ -268,7 +268,7 @@ impl Pool {
 		header: &BlockHeader,
 	) -> Result<BlockSums, PoolError> {
 		let overage = tx.overage();
-		let offset = (header.total_kernel_offset() + tx.offset)?;
+		let offset = (header.total_kernel_offset() + tx.offset.clone())?;
 
 		let block_sums = self.blockchain.get_block_sums(&header.hash())?;