Fix FX3 memory query filter limit on large fabrics

[monrog2]

Summary

• replace the per-FX3-node APIC filter with one constant-size procMemUsage query
• filter the below-32GB response locally against the affected FX3 node IDs already present in fabric_nodes
• add regression coverage for 55 affected nodes and for excluding low-memory non-FX3 switches

Validation

• python3 -m pytest tests/checks/n9k_c93180yc_fx3_switch_memory_check/test_n9k_c93180yc_fx3_switch_memory_check.py (7 passed)
• python3 -m pytest (1004 passed)
• GitLab integration pipeline 208, actual-current-version job 698: scale1 completed with 104 fabric nodes and 52 affected FX3 nodes; the constant-size query returned 7 below-threshold supervisor records, none from affected FX3 nodes; the check passed with no APIC 301/filter-expression-limit error

Fixes #423