Fixes <https://bugs.gnu.org/35582>.
Reported by sirgazil <sirgazil@zoho.com>.
Previously, leading zeros would be removed, leading to an "invalid"
UUID:
(uuid->string (uuid "00CA-050E" 'fat32))
⇒ "CA-50E"
(string->uuid "CA-50E" 'fat32)
⇒ #f
* gnu/system/uuid.scm (fat-uuid->string): Pad digits with zeros.
* tests/uuid.scm ("uuid, FAT32, leading zeros preserved"): New test.
* gnu/system/uuid.scm (uuid=?): New procedure.
* tests/uuid.scm ("uuid=?"): New test.
* gnu/build/file-systems.scm (partition-uuid-predicate)
(luks-partition-uuid-predicate): Use it instead of 'bytevector=?'.
* gnu/system/uuid.scm (%fat32-uuid-rx): New variable.
(string->fat32-uuid): New procedure.
(%uuid-parsers): Add it.
* tests/uuid.scm ("uuid, FAT32, format preserved"): New test.