Possible error in stdlib field `decompose_into_bits`

[maramihali]

Hard-coded 127 might be incorrect when 128 < num_bits < 256

[ledwards2225]

@iakovenkos Flagging this as something to look into during your audit

[iakovenkos]

I removed the num_bits argument in AztecProtocol/aztec-packages#14413, cause I didn't find any non-test occurrences of this function with this argument explicitly specified