Fix CUSTOM_OBJFUNC support in Python layer

[riddhi1228]

This PR fixes the handling of CUSTOM_OBJFUNC in the Python interface.

Problem

When evaluating custom objective functions, the Python layer could raise
a KeyError because the header "Custom_ObjFunc" from history files was not
normalized to the expected "CUSTOM_OBJFUNC" key.

Solution

• Register CUSTOM_OBJFUNC in historyMap
• Normalize "Custom_ObjFunc" header to "CUSTOM_OBJFUNC"
• Ensure custom objective functions are correctly evaluated without KeyError

This resolves issue #2586.

[pcarruscag]

==================== Start Test: sphere_ffd_def_bspline ====================
/github/workspace/tests/TestCases/deformation/spherical_ffd
sphere_ffd_def_bspline: PASSED
execution command: SU2_DEF def_spherical_bspline.cfg > def_spherical_bspline.log 2>&1
test_iter=10
test_vals (stored): 0.002068
sim_vals (computed): 0.002068
delta_vals: 0.000000
test duration: 0.03 min
Traceback (most recent call last):
  File "/github/workspace/install/bin/continuous_adjoint.py", line 32, in <module>
    import SU2
  File "/github/workspace/install/bin/SU2/__init__.py", line 19, in <module>
    from SU2 import eval
  File "/github/workspace/install/bin/SU2/eval/__init__.py", line 1, in <module>
    from SU2.eval.functions import function as func
  File "/github/workspace/install/bin/SU2/eval/functions.py", line 92
    header_to_key = {v["HEADER"]: k for k, v in su2io.historyOutFields.items()}
    ^
IndentationError: unexpected indent

[riddhi1228]

Fixed — the indentation error on line 92 has been corrected and black formatting applied. Thanks for catching it.

[riddhi1228]

The black formatting check is failing on historyMap.py even though black 22.6.0 reports no changes needed locally and the file is unchanged on the develop branch. This appears to be a pre-existing formatting issue in the repo rather than something introduced by this PR. Happy to investigate further if you can point me to what the CI is reformatting exactly.

[pcarruscag]

It's ok. The bigger issue is that this historyMap.py file should be generated, not edited manually.
Can you try to run the script that generates the historyMap (it's somewhere in SU2_PY) and see if the tests still pass?