chore: checkpoint before Python removal

vendor/clap_builder/src/parser/matches/value_source.rs

@@ -0,0 +1,17 @@
+/// Origin of the argument's value
+#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord)]
+#[non_exhaustive]
+pub enum ValueSource {
+    /// Value came [`Arg::default_value`][crate::Arg::default_value]
+    DefaultValue,
+    /// Value came [`Arg::env`][crate::Arg::env]
+    EnvVariable,
+    /// Value was passed in on the command-line
+    CommandLine,
+}
+
+impl ValueSource {
+    pub(crate) fn is_explicit(self) -> bool {
+        self != Self::DefaultValue
+    }
+}