Changes many fields to required -- as far as we were able to figure out,
signing would fail if these fields aren't provided anyway, so this
should not pose a compatibility problem.
Co-authored-by: matejcik <ja@matejcik.cz>
also make a cleaner distinction between keychain, seed, path
This enables using `unsafe_prompts`, because with the original code, if
there was no namespace match, we wouldn't know which curve to use.
For ease of implementation, we use a LRU cache for derived keys,
instead of the original design "one cache entry per namespace".
SLIP21 is now treated completely separately, via `slip21_namespaces` and
`derive_slip21` method.
If more slip21-like things come in the future, we can instead hang them
on the keychain: put a per-curve Keychain object accessible by
`keychain[curve_name].derive()`, and the majority usecase will just pass
around `keychain[curve_name]` instead of having to specify the curve in
every `derive()` call.
Or alternately we'll just specify the curve in every `derive()` call,
whichever seems more appropriate.
