fix(acir): Extend slice on dynamic insertion and compilation panic when flattening

[vezenovm]

Description

Problem*

Resolves #10015
Resolves #10048

Summary*

We were not actually extended the slice in SliceInsert. We were simply directly inserting into the specified index.

• I fixed the final slice length calculation so we appropriately extend the slice on an insert.
• I made a new AcirContext::flatten method to handle when we need to guarantee flattened AcirValues in all cases (static and dynamic arrays).
• I used the new flatten method to consolidate the fixes for ACIR gen: Dynamic slice insert triggers unexpected OOB #10015 and ACIR gen: Dynamic slice insert of dynamic array element triggers compiler panic #10048. ACIR gen: Dynamic slice insert triggers unexpected OOB #10015 required updating the flat numeric types along with the slice length. With AcirContext::flatten we could easily handle moving away from AcirValue::flatten and updating the numeric types of the dynamic array.
• I updated the slice insert test. I also updated and simplified the slice remove test as some comments were off.

Additional Context

Documentation*

Check one:

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

PR Checklist*

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

[github-actions]

Changes to circuit sizes

Generated at commit: e6ec0d4ba1bd15da24146a335e292eab52fa8996, compared to commit: 7e4e32ff58c663e1963778d95990d95f126fa21c

🧾 Summary (10% most significant diffs)

Program	ACIR opcodes (+/-)	%	Circuit size (+/-)	%
slice_dynamic_index	+21 ❌	+2.61%	+28 ❌	+0.55%

---

Full diff report 👇

Program	ACIR opcodes (+/-)	%	Circuit size (+/-)	%
slice_dynamic_index	827 (+21)	+2.61%	5,099 (+28)	+0.55%

[github-actions]

⚠️ Performance Alert ⚠️

Possible performance regression was detected for benchmark 'Execution Time'.
Benchmark result of this commit is worse than the previous benchmark result exceeding threshold 1.20.

Benchmark suite	Current: 5437f9d	Previous: 7e4e32f	Ratio
rollup-checkpoint-merge	0.004 s	0.003 s	1.33
semaphore-depth-10	0.071 s	0.045 s	1.58

This comment was automatically generated by workflow using github-action-benchmark.

CC: @TomAFrench