feat: port NumberTheory.Modular (#5540)

Author: Komyyy

Mathlib.lean

@@ -2374,6 +2374,7 @@ import Mathlib.NumberTheory.Liouville.Measure
 import Mathlib.NumberTheory.Liouville.Residual
 import Mathlib.NumberTheory.LucasLehmer
 import Mathlib.NumberTheory.LucasPrimality
+import Mathlib.NumberTheory.Modular
 import Mathlib.NumberTheory.ModularForms.CongruenceSubgroups
 import Mathlib.NumberTheory.ModularForms.SlashActions
 import Mathlib.NumberTheory.ModularForms.SlashInvariantForms