GCC to 12.4, Newlib to 4.3.0, faster RP2350 libs (#2480)

Newlib built using `-Os` causes things like `memcpy` to be very slow on the
RP2350 because it uses byte-wise operations.  On the RP2040 this doesn't
matter because there is a ROM routine we use instead of the library, but on
the Pico 2 it's almost 10x slower than the optimal method.

Update GCC to 12.4
Update Newlib to 4.4.0
Move to -O2 library compilation

New toolchain looks to add ~10K to RP2350 flash usage (less on the RP2040).

Author: earlephilhower