There is a really convincing set of arguments against this idea by Robert Seacord[1]. I used to be in the signed size camp, but I've come around to preferring unsigned as much as possible because it's much easier to reason about. I think there are far more footguns than people realize when it comes to signed integers.
"Rust’s safety guarantees only cover what the program itself can do, and not what entities outside the program can do to it. /proc/self/mem is considered to be such an external entity..."
Anecdotally, Chrome used to pin my hard drive at 100% usage until I killed a process called "software_reporter_tool.exe." I still have a version of the binary located at "%localappdata%\Google\Chrome\User Data\SwReporter\107.294.200" last modified 2022-11-02.
[1] https://www.youtube.com/watch?v=82jVpEmAEV4