feat: early interface with Python

src/arbitrary/finite_f64.rs

@@ -0,0 +1,22 @@
+use snafu::Snafu;
+
+#[derive(Debug, Clone, derive_more::Into)]
+pub struct FiniteF64(f64);
+
+#[derive(Debug, Snafu)]
+#[snafu(display("{value:?} is not finite"))]
+pub struct NotFinite {
+    value: f64,
+}
+
+impl TryFrom<f64> for FiniteF64 {
+    type Error = NotFinite;
+
+    fn try_from(value: f64) -> Result<Self, Self::Error> {
+        if value.is_finite() {
+            Ok(Self(value))
+        } else {
+            Err(NotFinite { value })
+        }
+    }
+}