fix: avoid duplicating constant arrays

[guipublic]

Description

Problem*

Resolves #5286

Summary*

Keep track of constant arrays and the array they resolve to in mem2reg, so that another constant array is not created for the same array.

Additional Context

Documentation*

Check one:

• [X] No documentation needed.
• [ ] Documentation included in this PR.
• [ ] [For Experimental Features] Documentation to be submitted in a separate PR.

PR Checklist*

• [X] I have tested the changes locally.
• [X] I have formatted the changes with Prettier and/or cargo fmt on default settings.

[github-actions[bot]]

Changes to circuit sizes

Generated at commit: 7dfada018bc7e06bde533f1a46d2eb36db2de670, compared to commit: e1000176a31140b2abd79c47653cbc4bb1a6808a

🧾 Summary (10% most significant diffs)

Program	ACIR opcodes (+/-)	%	Circuit size (+/-)	%
nested_array_dynamic	+43 ❌	+0.98%	-616 ✅	-3.88%
nested_array_in_slice	+1 ❌	+0.09%	-984 ✅	-14.67%

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Full diff report 👇

| Program | ACIR opcodes (+/-) | % | Circuit size (+/-) | % | |:-|-:|-:|-:|-:| | **slice_dynamic_index** | 1,322 (+53) | **+4.18%** | 6,855 (-46) | **-0.67%** | | **hashmap** | 209,915 (-84) | **-0.04%** | 397,328 (-3,691) | **-0.92%** | | **nested_array_dynamic** | 4,449 (+43) | **+0.98%** | 15,257 (-616) | **-3.88%** | | **nested_array_in_slice** | 1,095 (+1) | **+0.09%** | 5,723 (-984) | **-14.67%** |