Implement [floor|ceil|trunc|round_ties_even|euclidean]_modulo QoIs

[juntyr]

• implement support for non-constant dividend p
• still require divisor q to be constant
• add fuzzing support
• can we combine all modulo expressions into one implementation? no
• review and refactor implementation
• add howto for derivatives, mentioning finite differences, periodic axes, how to manually do X[i+5]-X[i-5] and how to do manual periodic axes using round_ties_even_modulo