Deriving private keys from BIP32 paths, public keys from private keys,
scripts from public keys, and addresses from scripts are some of the
most CPU-intensive tasks the wallet performs. Once the wallet inevitably
accumulates thousands of used paths, startup times become painful due to
needing to re-derive these data items for every used path in the wallet
upon every startup. Introduce a persistent cache to avoid the need to
re-derive these items every time the wallet is opened.
Introduce _get_keypair_from_path and _get_pubkey_from_path methods to
allow cached public keys to be used rather than always deriving them on
the fly.
Change many code paths that were calling CPU-intensive methods of
BTCEngine so that instead they call _get_key_from_path,
_get_keypair_from_path, _get_pubkey_from_path, get_script_from_path,
and/or get_address_from_path, all of which can take advantage of the new
cache.
Matt Whitlock
5bc7eb4b8e