What is the ruling on one who fasted and prayed while in a state of major ritual impurity (junub) out of ignorance, and does the ruling differ between قصور (inability/shortcoming) and تقصير (negligence/dereliction)?

Ghusl al-janabah (ritual bath after sexual impurity) is a condition for the validity of prayer. Therefore, whoever prays while in a state of janabah has an invalid prayer, and it must be repeated due to the absence of one of the conditions of prayer, even if the worshipper was ignorant of that. He must make up for the prayers he missed.

As for fasting, purity is not a condition for its validity, and its abandonment, whether intentional or out of ignorance, does not invalidate it.