fix: Show output of test_program_is_idempotent on failure

[jfecher]

Description

Problem*

Resolves #6940

Summary*

Using par_iter prevents cargo t from capturing each threads output apparently. Switching back to iter shows any output, including the failing assert.

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]

Execution Report

Program	Execution Time	%
sha256_regression	0.590s	-2%
regression_4709	0.395s	-4%
ram_blowup_regression	3.864s	-2%
rollup-root	2.134s	-3%
rollup-block-merge	2.132s	1%
rollup-base-public	34.695s	-1%
rollup-base-private	31.658s	0%
private-kernel-tail	0.744s	-2%
private-kernel-reset	2.144s	-2%
private-kernel-inner	1.211s	-3%
parity-root	0.543s	1%

[github-actions]

Compilation Report

Program	Compilation Time	%
sha256_regression	1.351s	0%
regression_4709	0.800s	0%
ram_blowup_regression	15.181s	-1%
rollup-root	3.608s	-1%
rollup-block-merge	3.619s	0%
rollup-base-public	111.496s	-3%
rollup-base-private	95.715s	-2%
private-kernel-tail	1.000s	-6%
private-kernel-reset	7.197s	1%
private-kernel-inner	2.191s	-3%
parity-root	0.757s	4%
noir-contracts	85.850s	-2%

[github-actions]

Execution Memory Report

Program	Peak Memory
keccak256	74.61M
workspace	123.66M
regression_4709	315.92M
ram_blowup_regression	512.47M
rollup-base-public	3.05G
rollup-base-private	2.97G
private-kernel-tail	181.16M
private-kernel-reset	255.25M
private-kernel-inner	214.35M
parity-root	155.86M

[github-actions]

Compilation Memory Report

Program	Peak Memory
keccak256	78.48M
workspace	123.65M
regression_4709	422.91M
ram_blowup_regression	1.58G
rollup-base-public	10.47G
rollup-base-private	6.57G
private-kernel-tail	201.79M
private-kernel-reset	717.06M
private-kernel-inner	291.86M
parity-root	172.13M