Arduino-pico's lwIP defaults are tuned for general-purpose networking,
not IoT devices. This generates a custom lwipopts.h overlay using
#include_next to chain to the framework's original, then override
specific settings to match ESP32's lwIP tuning.
Saves ~12KB static RAM by reducing oversized buffer and pool defaults.
Tested on Pico W (CYW43 WiFi) and Wiznet W5500 (Ethernet) with
500-iteration concurrent connect/disconnect stress tests.
J. Nick Koston