fix CI: declare profile feature in check-cfg for newer Rust

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: PeaBrane

spin-sim/Cargo.toml

@@ -12,6 +12,9 @@ categories = ["science", "simulation"]
 [features]
 profile = []
 
+[lints.rust]
+unexpected_cfgs = { level = "warn", check-cfg = ['cfg(feature, values("profile"))'] }
+
 [dependencies]
 rand = "0.8"
 rand_xoshiro = "0.6"