ci: bump MSRV to 1.88 to satisfy time 0.3.47 requirement

time/time-core/time-macros now require rustc 1.88, which is more
recent than the previous 1.85 bump made for clap_lex's edition2024.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: nficano

.github/workflows/test.yml

@@ -40,8 +40,8 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        # MSRV is read from `Cargo.toml` (`rust-version = "1.85"`). Keep in sync.
-        rust: ["1.85", "stable"]
+        # MSRV is read from `Cargo.toml` (`rust-version = "1.88"`). Keep in sync.
+        rust: ["1.88", "stable"]
     steps:
       - name: Checkout
         uses: actions/checkout@v4

Cargo.toml

@@ -2,7 +2,7 @@
 name = "arcp"
 version = "0.1.0"
 edition = "2021"
-rust-version = "1.85"
+rust-version = "1.88"
 license = "MIT OR Apache-2.0"
 description = "Reference implementation of the Agent Runtime Control Protocol (ARCP) v1.0"
 repository = "https://github.com/nficano/arpc"