feat: add middleware check_witness

[ed255]

Complete the implementation of the check_witness function which checks that a witness assignment passes all the constraints from a middleware Circuit. The missing parts were:

• Simulate blind rows
• Check copy constraints
• Check lookups
• Check shuffles

I've tried to keep the implementation simple (compared to the MockProver). For now it panics instead of returning errors.

This function was previously defined in the p3_frontend but is now moved to halo2_debug so that it can be used anywhere.

[codecov-commenter]

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Codecov Report

Attention: Patch coverage is 59.52381% with 51 lines in your changes missing coverage. Please review.

Project coverage is 82.48%. Comparing base (bc857a7) to head (da4983e).

Files	Patch %	Lines
halo2_debug/src/check_witness.rs	58.19%	51 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #356 +/- ## ========================================== - Coverage 82.64% 82.48% -0.17% ========================================== Files 84 85 +1 Lines 17750 17832 +82 ========================================== + Hits 14670 14709 +39 - Misses 3080 3123 +43 ```

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