fix(fuzz): Assign to an index variable to sequence side effects

[aakoshh]

Description

Problem*

Resolves #9049

Summary*

Updates the AST fuzzer to create a temporary variable to hold the index when assigning to an array item, if the index expression can potentially have side effects. This is to match the sequencing of side effects in #8384

Additional Context

There was #8342 before the temporary variable was introduced, which ensured that RHS takes effect before LHS. However, the above PR was a meant to turn that around:

Jake: This is true, and it made the calculation consistent at the time (when SSA also used to evaluate rhs first), but the subsequent PR was meant to reverse that by breaking out lhs into a new statement evaluated before the assignment completely. So it should have reversed the order but seems it did not do so completely. I think as long as in lhs = rhs; we evaluate side-effects in the lhs before the ones in rhs we should be fine from a user-facing bug perspective then.

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]

⚠️ Performance Alert ⚠️

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

Benchmark suite	Current: b1392ec	Previous: 3838c69	Ratio
test_report_AztecProtocol_aztec-packages_noir-projects_aztec-nr	98 s	75 s	1.31
test_report_AztecProtocol_aztec-packages_noir-projects_noir-protocol-circuits_crates_types	91 s	73 s	1.25

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

CC: @TomAFrench