Mark Rust v1.88 as the lowest supported version

Pretty crazy that it just came out 3 days ago, because I am in fact
using a piece of syntax that does not compile with Rust v1.87: a `if
let` alongside an `if` statement.

    if !opts.raw && let Some(grep) = &opts.grep

This is "unstable" in previous versions of Rust and will not compile, so
we _must_ use Rust v1.88.

  [1]: rust-lang/rust#132833

Author: mdippery

Cargo.toml

@@ -2,6 +2,7 @@
 name = "usaidwat"
 version = "2.0.0-alpha.3"
 edition = "2024"
+rust-version = "1.88"
 
 [dependencies]
 chrono = { version = "0.4.41", features = ["serde"] }