fix: avoid cloning range proofs during verification

[AaronFeickert]

Description

Removes unnecessary cloning of range proofs during batch verification.

Motivation and Context

Currently, range proofs exist in transaction outputs as byte vectors. When parsing outputs to collect these proofs for batch verification, the byte vectors are cloned. This is done because the verification API requires that the vector of proofs contain a vector reference to each proof, but the BulletRangeProof type wrapper provides a slice instead as part of its ByteArray implementation. Because proofs are several hundred bytes and batches can be large, this cloning is wasteful.

This PR adds BulletRangeProof::as_vec, which returns the underlying range proof as a vector reference. Doing so lets us avoid the clone while collecting the range proofs.

How Has This Been Tested?

Existing tests pass.

What process can a PR reviewer use to test or verify this change?

Confirm that the change removes the cloning.

[github-actions]

Test Results (CI)

1 260 tests   1 260 ✅  12m 3s ⏱️
   39 suites      0 💤
    1 files        0 ❌

Results for commit 129fbe5.

[AaronFeickert]

While this approach seems to do the trick, it feels non-idiomatic to me. Is there a better design that wouldn't require the new as_vec, like some kind of refactoring?

[github-actions]

Test Results (Integration tests)

29 tests  +29   29 ✅ +29   12m 27s ⏱️ + 12m 27s
11 suites +11    0 💤 ± 0 
 2 files   + 2    0 ❌ ± 0 

Results for commit 129fbe5. ± Comparison against base commit f5860a8.