a376408d

By: Greg Pfeil <greg@technomadic.org>

zcash_transparent: Collapse the copies of `RIPEMD160(SHA256(_))`

The crate spelled this hash out inline in ten places across five modules,
in three different shapes: compared as `hash[..] != …[..]`, converted
with `.into()`, and dereferenced through `.as_ref()`. The preceding
commits added an eleventh copy in the PCZT test helpers, which is what
brought it to notice.

A `pub(crate) hash160` in the crate root replaces all of them, and lets
each call site compare `[u8; 20]` values directly rather than slicing
both sides. The `ripemd` and `sha2` imports that existed only to spell it
out — including two `use` statements inside `match` arms in `builder.rs`
— go with them.

No behavioural change, and no CHANGELOG entry: the helper is private and
nothing observable moves. `zcash_transparent` 37 tests, `pczt` 11 + 4,
clippy clean with `--all-features --all-targets` and with
`--no-default-features`.

Timeline