Fix LICH Decode

This update fixes a defect in LICH decoding that prevented demod of in-progress or interrupted M17 streams. It also improves decoding of back-to-back streams, addressing a defect in the M17 state machine. Memory handling changes were made to handle stack size issues encountered during a compiler upgrade (to GCC 10.2). C++20 support is now required of the compiler (for std::span).

This release also includes fixes to reduce symbol jitter. Clocks, DAC timing and interrupt priorities were optimized to improve symbol timing. The modulator RRC was changed to use floating point.

Send link setup frame if M17 encoder is starved. This improves M17 audio streaming quality and prevents drops due to intermittent packet drops or jitter. This is less of an issue on NucleoTNC than with TNC3 over BLE.