mfsk-core 0.5.3

Pure-Rust WSJT-family decoders and synthesisers (FT8 FT4 FST4 WSPR JT9 JT65 Q65) behind a zero-cost Protocol trait. Host (rustfft) or no_std embedded targets (ESP32-S3, RP2350, Cortex-M) via a pluggable FFT backend; optional fixed-point hot path for FPU-less MCUs.