Fix DV_VALUE replacement bug in config.py (issue #2005)

[aryab08]

Summary

Fixes #2005 - Python scripts were replacing multi-value DV_VALUE parameters with zeros, causing solver crashes.

• Initialize DV_VALUE_NEW and DV_VALUE_OLD from existing DV_VALUE
• Prevents replacement of multi-value DV_VALUE with default [0]
• Fixes error: 'DV_VALUE does not contain enough entries to match DV_KIND or DV_PARAM'

The bug occurred when DV_VALUE_NEW/OLD were missing - they were initialized to [0] and then overwrote the original DV_VALUE. Now they inherit from DV_VALUE if it exists, preserving the original values.

Proposed Changes

This PR fixes a bug in config.py where design variable values were being incorrectly overwritten. The issue was in the initialization logic for DV_VALUE_NEW and DV_VALUE_OLD - they were hardcoded to [0], which would then replace the original multi-value DV_VALUE parameter.

Changes made:

• Modified lines 732 and 734 in SU2_PY/SU2/io/config.py
• Changed data_dict["DV_VALUE_NEW"] = [0] to data_dict["DV_VALUE_NEW"] = data_dict.get("DV_VALUE", [0])
• Changed data_dict["DV_VALUE_OLD"] = [0] to data_dict["DV_VALUE_OLD"] = data_dict.get("DV_VALUE", [0])

Testing:
Verified with the RAE2822 turbulent test case that:

• Before fix: DV_VALUE = 0 (incorrect - lost all 6 values)
• After fix: DV_VALUE = 0.02, 0.04, 0.06, 0.08, 0.1, 0.12 (correct - preserved all values)

Related Work

Closes #2005

This issue was originally reported by @jannav984 who identified the problematic code sections. Credit to them for the investigation work.

PR Checklist

• 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.