PADS_BANK0 GPIO5 had PDE (pull-down enable, bit 2) still set to its
reset default. With both PUE and PDE active the pin floated to ~VDD/2,
causing the Schmitt trigger to read LOW permanently. Clear PDE in
_configure_pad() so the pull-up works correctly.
Added PADS_BANK0_PDE_SHIFT define to rp2350.h.
No project uses floating-point, so coprocessor_enable() was dead code.
Removes rp2350_coprocessor.c/.h and all references from reset handlers
and Makefiles across all 15 CBM drivers (0x01-0x0f).