Extracts the key fingerprint from a BIP380 descriptor string.
The fingerprint is part of the key origin information, enclosed in square brackets
followed by a derivation path and a slash, as defined in BIP380.
Parameters
descriptor: string
The BIP380 descriptor string to parse.
Returns null|string
The extracted fingerprint as a lowercase hex string, or null if not found.
Extracts the key fingerprint from a BIP380 descriptor string. The fingerprint is part of the key origin information, enclosed in square brackets followed by a derivation path and a slash, as defined in BIP380.