fix(dsl): Assume block constraint is only using new witness

[guipublic]

Description

We assume block constraints uses only new witness for index and value of memory operation. This makes it easier to handle cases without witness assignment. For instance, before we could get w-3 which would evaluate to -3 and lead to invalid index.

This PR is required for dynamic arrays in noir.

Checklist:

• I have reviewed my diff in github, line by line.
• Every change is related to the PR description.
• I have linked this pull request to the issue(s) that it resolves.
• There are no unexpected formatting changes, superfluous debug logs, or commented-out code.
• There are no circuit changes, OR specifications in /markdown/specs have been updated.
• There are no circuit changes, OR a cryptographer has been assigned for review.
• I've updated any terraform that needs updating (e.g. environment variables) for deployment.
• The branch has been rebased against the head of its merge target.
• I'm happy for the PR to be merged at the reviewer's next convenience.
• New functions, classes, etc. have been documented according to the doxygen comment format. Classes and structs must have @brief describing the intended functionality.
• If existing code has been modified, such documentation has been added or updated.

[vezenovm]

Looks good, I've re-ran the failing circuits x86 tests

[TomAFrench]

This breaks the acir-format tests (see #570) although this isn't shown as these weren't being checked in CI at the time of this PR.