fix: audit protocol handling

[abonander]

Fixes #3440

Resolves https://rustsec.org/advisories/RUSTSEC-2024-0363.html

The last three commits may be cherry-picked against 6f29056 to see the exploit in action.

As of writing, only the Postgres driver actually appears to be exploitable before this patch, and appears to no longer be exploitable afterwards.

[FSMaxB]

I know this might be undesirable because it costs performance, but the pattern that I usually follow for these kinds of casts is SmallerIntegerType::try_from(bigger_integer_value).unwrap_or_else(|| unreachable!("Can't fail because <insert reason>"))

[abonander]

For the most part, I'm trying to avoid panics because they've caused issues before. Trying to encode too large of a value is generally a recoverable error.