Remove `num_bits_buffered`

[dominformant]

In my opinion, num_bits_buffered is no longer required. For timing, we now have num_bits_after_valid_subframe, which is actually more precise and searching for preambles after each bit would ease handling missed bits. Regarding the performance, I think we can spend the time on the additional preamble searches.

GNSSDecoder.jl/src/gpsl1_structs.jl

Lines 202 to 203 in 8550134

	num_bits_buffered::Int = 0
	num_bits_after_valid_subframe::Int = 0