Add error and range-checking parsers for unsigned 32 and 64 bit numbers.
The 32-bit variant is required for parsing sequence numbers from the
command line in `bitcoin-tx` (see #8164 for discussion). I've thrown in
the 64-bit variant as a bonus, as I'm sure it will be needed at some
point.
Also adds tests, and updates `developer-notes.md`.
I've collected these over time, mostly adding notes after
troubleshooting obscure bugs. As I hope to get the community more
involved in the whole process, I think it is useful to add to the
developer-notes.
