[Hotfix Main]: [FXC-5244] fix(): Added validator for write_single_file to surface output

[github-actions]

Hotfix of PR #1756 (#1756) to the main branch.
Hey @piotrkluba, please review this hotfix PR created from your original PR.

⚠️ Note: This PR had conflicts with the base branch and was resolved automatically. Please review the changes carefully.

---

Note

Low Risk
Small, localized validation change that only affects parameter construction/validation for surface outputs; primary risk is stricter validation breaking previously-accepted (but unsupported) configs.

Overview
Adds a SurfaceOutput model-level validator that enforces write_single_file can only be used with Tecplot output: it now errors for output_format="paraview" and emits a validation warning for output_format="both" (Tecplot single file + separate Paraview files).

Updates/extends tests to cover the new validator behavior and adjusts existing fixtures/usages to explicitly set output_format="tecplot" where write_single_file=True to keep tests valid.

^{Written by Cursor Bugbot for commit bfbf098. This will update automatically on new commits. Configure here.}

[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

^{Bugbot Autofix is OFF. To automatically fix reported issues with Cloud Agents, enable Autofix in the Cursor dashboard.}