Set pylists to expected size on creation
Slightly rework error checking when deserializing buffer
As discussed in !125 (merged), we're considering setting the size of PyList on creation, rather than have it resizing on each appended PostcohInspiralTable.
I've tried doing the same for wrapped_snr_series_list, but it's a much lower priority. The tradeoff between readability/simplicity and optimising may not be there for that change.