Fix baseexport: serialize hetero delays, capture resolved integrator, handle NetworkOperation

[Sanchit2662]

Summary

I was going through the baseexport collector and found three issues that were silently breaking things.

The first one was in collect_Synapses. The delay was only being serialized when it was a scalar value (single delay for all synapses). If you had per-synapse delays like S.delay = 'rand() * 5*ms', that condition would be false and the entire delay array would just get dropped from the export with no warning. The fix is literally removing that condition. obj.delay[:] works fine for both scalar and array cases, so there was no reason to guard it in the first place.

The second one was in collect_NeuronGroup and collect_SpatialNeuron. When a user doesn't specify a method explicitly, Brian2 still picks one at runtime (like exact or exponential_euler) but we were just storing None in the export. There was even a TODO comment there acknowledging it. I fixed it by looking at the StateUpdater object's method_choice during the contained objects loop, where the runtime-resolved method is actually available. It gets stored as resolved_method so an importer can explicitly set the same integrator rather than relying on Brian2's auto-selection which might differ across versions.

The third one was NetworkOperation. If you had a @network_operation in your network, the exporter would just crash with a NotImplementedError. I added NetworkOperation to supported_objs so it no longer blows up, wrote a collect_NetworkOperation function that captures the scheduling metadata (name, dt, when, eorder), and added a logger warning so the user knows the function body itself isn't captured. It's honest about what it can and can't do rather than just crashing.

[Sanchit2662]

Hi @mstimberg , please review the changes.

[mstimberg]

Hi @Sanchit2662. These additions do sound useful, but did you actually try running your code? There is an incorrect import, and I don't think the obj.delay[:] access will work in practice. Actually, heterogeneous delays were already captured in the serialization thanks to the generic "initializer" mechanism. E.g. for your example, the basexporter dictionary would contain:

{'index': 'True',
'source': 'synapses_pre',
'type': 'initializer',
'value': 'rand() * 5*ms',
'variable': 'delay'}

inside the 'initializers_connectors' key.

[Sanchit2662]

Hi @mstimberg , I have made the changes.

[mstimberg]

Hi @Sanchit2662. Could you please merge latest master into this branch. The test suite should not be failing any more then.