Improvements to SWIG typemaps for Python interface

[oskooi]

Various improvements to the SWIG typemaps for the Python interface, organized by priority.

Critical — Crash/Segfault Bugs

1. Missing NULL checks in callback wrappers (meep.i)

py_callback_wrap (line 142), py_amp_func_wrap (line 152), and custom_py_src_time::dipole (meep-python.hpp:32) do not check the return value of PyObject_CallFunctionObjArgs. If the Python callback raises an exception, these dereference NULL →segfault. Same issue in mpb.i callback wrappers.

2. Use-after-free in _get_dft_array (meep.i:456)

The rank == 0 zero-data path passes a stack-allocated d[1] to PyArray_SimpleNewFromData, which creates a NumPy array pointing to stack memory that goes out of scope. The singleton path also leaks dft_arr.

High Priority — Correctness

3. meep::abort() instead of Python exceptions (typemap_utils.cpp)

Many conversion functions (e.g., pyabsorber_to_absorber, pymaterial_grid_to_material_grid, py_list_to_gobj_list) call abort_with_stack_trace() on invalid input. This kills the process instead of raising a catchable Python exception. These should set PyErr_SetString and return an error code.

4. PyFunction_Check vs PyCallable_Check (meep.i:1408)

The kpoint_func typemap rejects lambdas, bound methods, functools.portal, and any callable that isn't a plain function. Should use PyCallable_Check.

Medium Priority — Maintenance & Compatibility

5. Dupilcate typemaps

• xtics/ytics/ztics typemaps appear twice (lines 1001-1018 and 1083-1105), first block is dead code.
• freearg for amplitude function appears twice (lines 748 and 1069).
• double* array input typemaps repeat the same is_array + array_data pattern ~8 times - could use %apply.

Low Priority — Cleanup

6. Duplicate %ignore directives (meep.i:1525-1529)

is_variable, is_file, is_medium each ignored twice.

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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 73.87%. Comparing base (f29a8c7) to head (f2821a2).
⚠️ Report is 120 commits behind head on master.
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Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3190      +/-   ##
==========================================
+ Coverage   73.81%   73.87%   +0.05%     
==========================================
  Files          18       18              
  Lines        5423     5458      +35     
==========================================
+ Hits         4003     4032      +29     
- Misses       1420     1426       +6     

see 2 files with indirect coverage changes

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