feat: Implement compute_shuffled_index in plonky2x and add abstracted functions for plonky2x in the utils file

[NikolayKostadinov21]

Rewrite compute_shuffled_index in plonky2x. Implement utils folder containing abstracted functions in plonky2x.

[Owliie]

Run formatter for rust files

[Xearty]

Think about moving utils.rs and variable.rs to plonky2x_extensions

[Xearty]

Rename compute_shuffled_index.rs to circuit.rs

[Xearty]

Export the circuit struct from the mod and make the circuit module private akin to weigh_justification_and_finalization