Update to Rust 2024 Edition / MSRV of 1.85

[notpeter]

Proposing updating Dropshot to Rust 2024 Edition and explicitly specifying 1.85 as MSRV.

I would propose this is done as distinct PRs:

1. PR with Automated formatting and edition changes: cargo fix --edition and cargo fmt with style_edition = 2024 in rustfmt.toml. Rust 2024 Edition - Fixing and formating #1605

2. PR which:
   a. Changes the Cargo.toml edition to 2024
   b. Expands the CI matrix to run under a "current" rust version (rust-toolchain.toml) and under the MSRV (rust 1.85)

3. PR adding .git-blame-ignore-revs to ignore the commit hash from the first PR.

GitHub will automatically pickup .git-blame-ignore-revs when calculating blame (no config required). I usually add instructions to the file to for how to configure git locally (like this one).

Thoughts?
CC: @ahl @sunshowers

Prior work:

• migrate to Rust 2024 #1439