[DNMY] Serialize NetworkReduction Data

[jd-lara]

This commit implements comprehensive serialization and deserialization of NetworkReductionData within PTDF HDF5 files, addressing the issue where network reduction maps were lost during serialization, rendering the PowerNetworkMatrices less useful.

Changes:

• Extended to_hdf5() to serialize NetworkReductionData fields
• Extended from_hdf5() to deserialize NetworkReductionData
• Added JSON3 import for handling complex nested data structures
• Implemented helper functions for serializing:
  • Simple sets and dictionaries (bus maps, removed buses/arcs)
  • Complex dictionaries with tuple keys and complex values
  • Bus reduction maps and reverse search maps
  • Added branch and admittance maps
  • Branch metadata (direct, parallel, series, transformer3W)
  • ReductionContainer with all reduction types

Implementation Details:

• Uses HDF5 groups to organize network reduction data hierarchically
• Employs JSON3 for serializing complex nested structures
• Preserves network topology information (bus/arc mappings)
• Stores metadata about PSY objects (names, types) where full object serialization is not feasible
• Maintains backward compatibility with existing HDF5 files
• Empty NetworkReductionData is handled efficiently

Limitations:

• PSY object references (ACTransmission, ThreeWindingTransformer) are not fully serialized, only their metadata
• Reverse maps (reverse_direct_branch_map, etc.) are preserved as empty since they contain PSY objects as keys
• Derived fields (all_branch_maps_by_type, name_to_arc_map) are not serialized and should be repopulated if needed

Testing:

• Added comprehensive test suite in test_network_reduction_serialization.jl
• Tests cover RadialReduction, DegreeTwoReduction, and combined reductions
• Verifies topology preservation, compression compatibility, and backward compatibility

Fixes issue where PowerNetworkMatrices became less useful after deserialization due to lost network reduction information.

Thanks for opening a PR to PowerNetworkMatrices.jl, please take note of the following when making a PR:

Check the contributor guidelines

[jd-lara]

@copilot review the code errors in the getter function that is failing in the tests and make a correction to the tests. Check the logs from the GitHub actions.

[Copilot]

@jd-lara I've opened a new pull request, #209, to work on those changes. Once the pull request is ready, I'll request review from you.