settings: do not store "debug.randomness-seed" in stringified form

While this is a debug option, it doesn't make sense to store an integer value
as a string. We can parse the environment variable instead. The variable is
temporarily parsed into i64 because i64 is the integer type of TOML.
toml_edit::Value doesn't implement any other integer conversion functions.

cli/src/config.rs

@@ -411,7 +411,7 @@ fn env_overrides() -> config::Config {
             .set_override("debug.commit-timestamp", value)
             .unwrap();
     }
-    if let Ok(value) = env::var("JJ_RANDOMNESS_SEED") {
+    if let Ok(Ok(value)) = env::var("JJ_RANDOMNESS_SEED").map(|s| s.parse::<i64>()) {
         builder = builder
             .set_override("debug.randomness-seed", value)
             .unwrap();

lib/src/settings.rs

@@ -132,17 +132,10 @@ fn get_timestamp_config(config: &StackedConfig, key: &'static str) -> Option<Tim
     }
 }
 
-fn get_rng_seed_config(config: &StackedConfig) -> Option<u64> {
-    config
-        .get::<String>("debug.randomness-seed")
-        .ok()
-        .and_then(|str| str.parse().ok())
-}
-
 impl UserSettings {
     pub fn from_config(config: StackedConfig) -> Self {
         let timestamp = get_timestamp_config(&config, "debug.commit-timestamp");
-        let rng_seed = get_rng_seed_config(&config);
+        let rng_seed = config.get::<u64>("debug.randomness-seed").ok();
         UserSettings {
             config,
             timestamp,

lib/testutils/src/lib.rs

@@ -112,7 +112,7 @@ pub fn base_user_config() -> StackedConfig {
         user.email = "test.user@example.com"
         operation.username = "test-username"
         operation.hostname = "host.example.com"
-        debug.randomness-seed = "42"
+        debug.randomness-seed = 42
     "#;
     let mut config = StackedConfig::empty();
     config.add_layer(ConfigLayer::parse(ConfigSource::User, config_text).unwrap());