Improve `periodic_column` usage in Plonky3 backend

[Leo-Besancon]

What should be done?

This issue is a followup on #461

As Plonky3 currently does not support periodic columns out of the box, we've introduced in #461 multiple structs and implementation for their support in our backend.

However, their handling can be improved. For instance, we can no longer prove or verify traces, only check that a given trace follows the constraints described in the Air for testing.

How should it be done?

• fn periodic_columns(&self) -> Vec<Self::PeriodicColumnsVar> { in AirBuilderWithPeriodicColumns should maybe return an Array

• periodic_columns in the DebugConstraintBuilderWithPeriodicColumns struct a bit differently

  • Pad all periodic columns to the maximum length by periodic repetition
  • Transpose the columns so that we have a vector of rows.
  • We just return &self.periodic_columns[self.row_index % col.len()]

_Originally posted by @adr1anh in #461 (comment)

• Add support of prove and verify

When is this task done?

This task is done when a better handling of periodic columns has been achieved and tested in all the current tests.

Additional context

No response