Is one who dies unjustly in prison due to poor conditions considered a martyr, and what are the rulings pertaining thereto?

A consensus of scholars has affirmed that whoever is wrongfully killed is a martyr. Examples of wrongful killing include: those killed by thieves, rebels, or highwaymen; those killed while defending themselves, their property, their life, their religion, their family, Muslims, or Ahl al-Dhimma (protected non-Muslims); or those killed for no wrongdoing, or who die in prison after being unjustly incarcerated.

Whoever is wrongfully killed should be washed, shrouded, and prayed over, as was done for Umar and Uthman, may Allah be pleased with them both.