Minor: MerkleProver::commit doesn't panic if the columns are not sorted in descending order

[weikengchen]

The comment of the commit method of MerkleProver says (https://github.com/starkware-libs/stwo/blob/dev/crates/prover/src/core/vcs/prover.rs#L24):

/// # Panics
///
/// This function will panic if the columns are not sorted in descending order or if the columns
/// vector is empty.

However, this doesn't seem to be the case, as the method doesn't panic, but indeed, it sorts the input column vectors through "sorted_by_key" (with a Reverse).

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