fix: bump CI Rust to 1.88 (let-chains stabilized in 1.88, not 1.87)

let_chains was stabilized in Rust 1.88.0 for edition 2024, per
rust-lang/rust#132833. 1.87 still reports them as unstable.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: thrashr888

.github/workflows/ci.yml

@@ -8,8 +8,8 @@ on:
 
 env:
   CARGO_TERM_COLOR: always
-  # Rust 1.87+ required for let-chains (edition 2024)
-  RUST_VERSION: "1.87"
+  # Rust 1.88+ required for let-chains (edition 2024)
+  RUST_VERSION: "1.88"
 
 jobs:
   check:

.github/workflows/release.yml

@@ -7,8 +7,8 @@ on:
 
 env:
   CARGO_TERM_COLOR: always
-  # Rust 1.87+ required for let-chains (edition 2024)
-  RUST_VERSION: "1.87"
+  # Rust 1.88+ required for let-chains (edition 2024)
+  RUST_VERSION: "1.88"
 
 permissions:
   contents: write