incremental changes

[abhijit-mudigonda]

• load precomputed higher weight spaces during during HeckeStability
• function to check if a form can be coerced into a smaller coefficient ring
• avoid the expensive check to test if the Grossencharacter torsor is nonempty if the infinity type is trivial on units
• add an option to allow primes dividing the level in Eigenbasis (useful when applying to a subspace of newforms)