Feature: Add Iteration Wall-Clock Timing (ITER_TIME)

[Soumyadipta-Banerjee]

Proposed Changes

This pull request introduces the ITER_TIME field, which prints the physical wall-clock time elapsed during the inner iteration step as an optional diagnostic column.

• Uses SU2_MPI::Wtime() synchronously across ranks to capture precise delta times between iteration steps.
• Designed as an opt-in metric via SCREEN_OUTPUT or HISTORY_OUTPUT configuration properties. It does not clutter the default console arrays, protecting the TestCases baseline reference setups in the CI pipeline.
• Handles padding organically aligned to ScreenOutputFormat::FIXED to retain the tight aesthetic tracking without jitter.

Related Work

N/A

PR Checklist

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• I am submitting my contribution to the develop branch.
• My contribution generates no new compiler warnings (try with --warnlevel=3 when using meson).
• My contribution is commented and consistent with SU2 style (https://su2code.github.io/docs_v7/Style-Guide/).
• I used the pre-commit hook to prevent dirty commits and used pre-commit run --all to format old commits.
• I have added a test case that demonstrates my contribution, if necessary.
• I have updated appropriate documentation (Tutorials, Docs Page, config_template.cpp), if necessary.