cbfddb0394 hashes: Rename length field and use u64 (Tobin C. Harding)
Pull request description:
The hash engine types have a `length` field that is used to cache the number of bytes hashed so far, as such it is an arbitrary number and could use a `u64` instead of `usize`.
While we are at it rename `length` to `bytes_hashed` to remove any ambiguity of what this field is. Note this field is private, we already have the public getter `n_bytes_hashes` to get the value.
Introduce a private function `incomplete_block_size`, the purpose of this function is to put all the casts in one place so they can be well documented and easily understood.
Fix: #3016
ACKs for top commit:
apoelstra:
ACK cbfddb0394 successfully ran local tests
Tree-SHA512: a9d932938afcbd6dfb9db471a02fa7e3fff8f0659906627001ad241390b9af57088fd34afeae551c70c2c49783e6296f110b57ff9de6fed2609f4648ec8fd934
76ea4eb400