Delegate derive_bip32_key to upstream LWK

[ok300]

Create a LWK PR to encapsulate and expose derive_bip32_key.

Once implemented, this should replace our OnchainWallet::derive_bip32_key.

This will allow us to not work with the seed directly when during LNURL-auth.

[LeoComandini]

Blockstream/lwk@f6c24d6

will be available in next release

[ok300]

Nice! Thanks @LeoComandini

[ok300]

We updated to the latest LWK, but the new LWK derive_xprv uses structs in bitcoin crate v0.31.2.

sdk-common uses structs from bitcoin crate v0.29.2 for compatibility with GL / VLS.

Unfortunately they're not compatible, so we'll have to wait until GL / VLS update to at least v0.31.2. Another option is to manually convert between the structs, but that's a lot of boilerplate and it touches many inner structs.

[dangeross]

Signer trait makes this redundant