Add foldhash crate to third-party deps

Author: dtolnay

third-party/Cargo.lock

@@ -10,6 +10,7 @@ rust-version = "1.77"
 cc = "1.0.83"
 clap = { version = "4", default-features = false, features = ["error-context", "help", "std", "usage"] }
 codespan-reporting = "0.11.1"
+foldhash = "0.1"
 proc-macro2 = { version = "1.0.58", features = ["span-locations"] }
 quote = "1.0.4"
 rustversion = "1"