Integer arithmetic/casting audit

[cole-miller]

No description provided.

[cole-miller]

I've eliminated unchecked integer arithmetic from sndjvu_format::ser, except for a few innocuous uses:

workspace/crates/sndjvu_format/src/ser.rs

Line 7 in eecf635

#![deny(clippy::integer_arithmetic)]

This is important because most of the arithmetic in that module goes to calculating values for various length/offset fields in the transfer format, and if one of those calculations overflows we want to signal an error rather than serialize a broken document.