MSO: Reduce data size

Since oscilloscope is using a 10 bit ADC (max 16 bits), use float32 instead of float64 for data representation: float32 has a 23-bit mantissa, already more precise than the super-precision mode (14 bits) of the scope. Time representation also doesn't need 52 bits of precision: maximum number of points recorded per waveform is 1M, so roughly 20 bits.