python: handle FpError::ZivRetryLimitExceeded in the bindings

The new float error variant (a Ziv loop that exhausts its retry budget, only
reachable if a radius bound is wrong) was missing from the two FpResult→PyResult
matches, so the python crate failed to compile since 50e7b3d. It now raises
RuntimeError (not a user-facing Python error, but a "please report this" case).

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

Author: Jacob Zhong

python/CHANGELOG.md

@@ -2,6 +2,11 @@
 
 ## Unreleased
 
+### Fix
+- The bindings now handle `dashu-float`'s new `FpError::ZivRetryLimitExceeded` (a Ziv loop that
+  exhausts its retry budget — only possible if a radius bound is wrong) — it raises `RuntimeError`
+  instead of failing to compile on a non-exhaustive match.
+
 ## 0.6.0
 
 ### Add

python/src/cache.rs

@@ -15,7 +15,7 @@ use std::cell::RefCell;
 
 use dashu::base::Sign;
 use dashu::float::{ConstCache, Context, FBig, FpError, FpResult, Repr, Word, round::Round};
-use pyo3::exceptions::{PyValueError, PyZeroDivisionError};
+use pyo3::exceptions::{PyRuntimeError, PyValueError, PyZeroDivisionError};
 use pyo3::prelude::*;
 
 thread_local! {
@@ -61,6 +61,12 @@ pub fn unwrap_float<R: Round, const B: Word>(
         Err(FpError::Indeterminate) => {
             Err(PyZeroDivisionError::new_err("indeterminate form (0/0)"))
         }
+        Err(FpError::ZivRetryLimitExceeded) => Err(PyRuntimeError::new_err(
+            "the Ziv retry limit was exceeded; the result is not correctly rounded (please report this case to the maintainer)",
+        )),
+        Err(FpError::ZivRetryLimitExceeded) => Err(PyRuntimeError::new_err(
+            "the Ziv retry limit was exceeded; the result is not correctly rounded (please report this case to the maintainer)",
+        )),
     }
 }
 
@@ -88,6 +94,12 @@ pub fn unwrap_complex<R: Round, const B: Word>(
         Err(FpError::Indeterminate) => {
             Err(PyZeroDivisionError::new_err("indeterminate form (0/0)"))
         }
+        Err(FpError::ZivRetryLimitExceeded) => Err(PyRuntimeError::new_err(
+            "the Ziv retry limit was exceeded; the result is not correctly rounded (please report this case to the maintainer)",
+        )),
+        Err(FpError::ZivRetryLimitExceeded) => Err(PyRuntimeError::new_err(
+            "the Ziv retry limit was exceeded; the result is not correctly rounded (please report this case to the maintainer)",
+        )),
     }
 }