Decide whether to increment MSRV for Arti 1.0.0

When we release, we will have an opportunity to increase our MSRV as high as 1.59, if we want.

Is there a reason to do so? The only other tickets we have that say "do such-and-such once we require Rust X" are labeled with ~"MSRV:1.60". So the only reason to do this would be for access to recent language and stdlib features.

The most relevant such features are, FWICT:

• Support for "Captured identifiers in format strings", as in println!("Hello, {person}!"). We run into this a lot by accident, and it seems to be a leading breaker of our minimal-version CI.
• "Custom cargo profiles", as in "Production" is based on "release", but with lto turned on.

IMO these features are not enough to justify an MSRV bump right now, but I thought I should ask.

@eta, @Diziet, does either of you think we should bump MSRV? If not, I'll close this.