Improved class aggregation for upstream/downstream connectivity queries

[Clare72]

No description provided.

[Robbie1977]

@Clare72 Can you add tests to https://github.com/VirtualFlyBrain/VFBquery/blob/main/.github/workflows/performance-test.yml

[Clare72]

Tests that exist but aren't wired into CI

Five connectivity test files in src/test/:

File	What it covers	In performance job?	In python-test job?
test_neuron_neuron_connectivity.py	per-neuron	partly (via test_query_performance's test_07)	no
test_neuron_region_connectivity.py	per-neuron	partly (via test_07)	no
test_upstream_class_connectivity.py	class-level	no	no
test_downstream_class_connectivity.py	class-level	no	no
test_vfb_connectivity.py	query_connectivity (cross-dataset)	no	no

The other CI workflow (python-test.yml) only runs term_info_queries_test.py.

So the three connectivity test files for the class-level and cross-dataset
queries are effectively orphaned — they'll only get exercised if someone runs
them locally.

Shall I add them all @Robbie1977 ?

[Robbie1977]

@Clare72 yes please

[Robbie1977]

@Clare72 Can you get Claude to check why the tests failed silently and resolve the errors shown in https://github.com/VirtualFlyBrain/VFBquery/actions/runs/26111178920/attempts/1#summary-76788537996