Transceiver52M: fix viterbi-eq soft bits on platforms where char is unsigned
The viterbi-eq demodulator stores soft bits into chars. "char" is signed on x86/amd64 but unsigned on arm64. On arm64 the stored byte 0x81 (== -127) is read back as +129, so after the sign flip and vectorSlicer() clamp every soft bit collapses to 0.0.
The same issue also appears to be present in the MS code path, so it was (blindly) fixed there as well. The MS fixes are untested!
