chore: replace deprecated tempdir crate with tempfile

The `tempdir` crate has been deprecated in favor of `tempfile`, which
now provides all the same functionality. This migration updates
varlink_generator's test dependencies to use `tempfile::TempDir`
instead of `tempdir::TempDir`.

API change: `TempDir::new("prefix")` → `TempDir::with_prefix("prefix")`

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

Author: haraldh

Cargo.lock

@@ -41,7 +41,6 @@ serde_derive = "1.0.102"
 serde_json = "1.0.41"
 static_assertions = "1.1.0"
 syn = "2.0"
-tempdir = "0.3.7"
 tempfile = "3.1.0"
 thiserror = "2.0.3"
 tokio = "1"

Cargo.toml

@@ -33,7 +33,7 @@ thiserror = { workspace = true }
 
 [dev-dependencies]
 unified-diff = { workspace = true }
-tempdir = { workspace = true }
+tempfile = { workspace = true }
 
 [badges]
 travis-ci = { repository = "varlink/rust" }

varlink_generator/Cargo.toml

@@ -3,7 +3,7 @@ extern crate varlink_generator;
 use std::fs;
 use std::io::prelude::*;
 use std::process::Command;
-use tempdir::TempDir;
+use tempfile::TempDir;
 use unified_diff::diff;
 
 #[cfg(unix)]
@@ -33,7 +33,7 @@ fn test_generate() {
         }
     }
 
-    let tmpdir = TempDir::new("test_generate").unwrap();
+    let tmpdir = TempDir::with_prefix("test_generate").unwrap();
 
     std::env::set_var("OUT_DIR", tmpdir.path().as_os_str());
     varlink_generator::cargo_build("tests/org.example.complex.varlink");