* fix: correct support for legacy hex keyfiles

* test: provide correct XMLv2 keyfile hash in test fixtures

* test: matrix test the cross tool compatibility

* fix: use KDBX3 UUID for AesKdf when serializing KDF parameters

fixes #357

KeePassXC has another non-standard UUID called the KDBX4 UUID for the
AES key derivation function, but it always writes the standard "KDBX3"
UUID for AesKdf, C9D9F39A628A4460BF740D08C18A4FEA