Update `PC::check_combinations` to optional rng

[vlopes11]

Summary

PC::check is implemented with optional rng:

poly-commit/src/lib.rs

Lines 225 to 233 in 9da67e2

	fn check<'a>(
	vk: &Self::VerifierKey,
	commitments: impl IntoIterator<Item = &'a LabeledCommitment<Self::Commitment>>,
	point: &'a P::Point,
	values: impl IntoIterator<Item = F>,
	proof: &Self::Proof,
	challenge_generator: &mut ChallengeGenerator<F, S>,
	rng: Option<&mut dyn RngCore>,
	) -> Result<bool, Self::Error>

However, rng is mandatory for check_combinations

poly-commit/src/lib.rs

Line 344 in 9da67e2

rng: &mut R,

Even tho PC::batch_check forwards that as optional

poly-commit/src/lib.rs

Line 292 in 9da67e2

Some(rng),

Problem Definition

This creates downstream conflicts for types that comply with PC::check and will have the rng as optional. In case the user will not provide the rng, we can defer to

poly-commit/src/optional_rng.rs

Line 12 in 9da67e2

impl<R: RngCore> RngCore for OptionalRng<R> {

Proposal

Update PC::check_combinations and PC::batch_check to take the rng as optional

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