Turn an unsigned integer into a signed one.

See https://en.wikipedia.org/wiki/Variable-length_quantity#Zigzag_encoding

skip slice off reads an integer at offset off, and returns how many bytes the integer occupies.

u64 slice off reads an integer at offset off, and returns a pair v, n_consumed. v is the read integer, n_consumed is the number of bytes consumed during reading.

Read a signed int64 by reading a u64 and zigzag decoding it

Like i64 but truncates to integer. Returns a pair v, n_consumed.

Like u64 but truncates to integer.