Quote the SU2 executable path in SU2_PY on Linux/macOS (SU2_RUN with spaces)

[nikita-ageev]

Proposed Changes

SU2_PY/SU2/run/interface.py builds the command as os.path.join(SU2_RUN, "SU2_CFD") + " config_CFD.cfg" and runs it with shell=True. The executable path is quoted only on Windows (quote = '"' if sys.platform == "win32" else ""), so on Linux/macOS any SU2_PY script (shape_optimization.py, parallel_computation.py, ...) fails if SU2_RUN contains a space.

This PR moves the quoting into build_command: the first word of the command is joined with SU2_RUN and quoted (shlex.quote on POSIX, double quotes on Windows as before), the callers pass plain "SU2_CFD config_CFD.cfg" strings. The quoted path is then inserted into the MPI template as before (mpirun -n %i %s, srun, SU2_MPI_COMMAND). The module-level quote variable is removed; it was not used outside interface.py.

Reproduction on macOS, SU2_RUN=".../su2 bin", shape_opt_euler_py from serial_regression.py:

before:
Command = /.../su2 bin/SU2_CFD config_CFD.cfg
SU2 process returned error '127'
/bin/sh: /.../su2: No such file or directory

after:
Command = '/.../su2 bin/SU2_CFD' config_CFD.cfg
optimization runs to the end

With the change and SU2_RUN containing a space, history_project.csv and the optimizer output of shape_opt_euler_py are identical to develop with a SU2_RUN without spaces. The MPI path was checked with NUMBER_PART=2: mpirun -n 2 '/.../su2 bin/SU2_CFD' config_CFD.cfg runs with 2 ranks. The Windows branch produces the same string as before.

Related Work

None found. Separate from #2934 (also SU2_PY).

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. — Not necessary: the change only affects how the executable path is quoted; shape_opt_euler_py passes unchanged, and the reproduction above (SU2_RUN with a space) fails before and passes after.
• I have updated appropriate documentation (Tutorials, Docs Page, config_template.cpp), if necessary. — Not necessary: no user-facing option changed.