SimultaneousState list saving was dropping FOVs (#97)

* SimultaneousState saving vec conversion bug

SimultaneousState.save_list was not working correctly due to a conversion order of operations issue.
The conversion between python and rust for list of SimultaneousStates was unintentionally dropping the FOV information.
This was leading to errors when attempting to save simulation results which included this information.

This was fixed by changing the order of operations to try SimState conversions before list conversions.
Error messages were edited to increase the clarity of the bug.

* changelog

CHANGELOG.md

@@ -18,6 +18,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - Field of View checks for states was optimized for multi-core processing on millions
   of objects, leading to huge speed gains for large queries.
+- Fixed a bug where saving lists of SimultaneousStates had a bug where field of view
+  information was not being saved correctly.
 
 ## [0.2.5] - 2024 - 8 - 12
 

src/neospy/rust/simult_states.rs

@@ -1,3 +1,4 @@
+use neospy_core::errors::Error;
 use neospy_core::io::FileIO;
 use neospy_core::simult_states;
 use pyo3::exceptions;
@@ -25,12 +26,18 @@ impl From<simult_states::SimultaneousStates> for PySimultaneousStates {
 
 impl<'py> FromPyObject<'py> for PySimultaneousStates {
     fn extract_bound(ob: &Bound<'py, PyAny>) -> PyResult<Self> {
-        if let Ok(states) = ob.extract::<Vec<PyState>>() {
-            return PySimultaneousStates::new(states, None);
+        match ob.downcast_exact::<PySimultaneousStates>() {
+            Ok(downcast) => Ok(PySimultaneousStates(downcast.get().0.clone())),
+            Err(_) => {
+                if let Ok(states) = ob.extract::<Vec<PyState>>() {
+                    PySimultaneousStates::new(states, None)
+                } else {
+                    Err(Error::ValueError(
+                        "Input could not be converted to a SimultaneousStates".into(),
+                    ))?
+                }
+            }
         }
-        Ok(PySimultaneousStates(
-            ob.downcast_exact::<PySimultaneousStates>()?.get().0.clone(),
-        ))
     }
 }
 

src/neospy_core/src/simult_states.rs

@@ -59,8 +59,11 @@ impl SimultaneousStates {
         {
             return Err(Error::ValueError("Center IDs do not match expected".into()));
         };
-        if fov.is_none() && !states.iter_mut().all(|state: &mut State| state.jd == jd) {
-            return Err(Error::ValueError("Epoch JDs do not match expected".into()));
+        if fov.is_none() && states.iter_mut().any(|state: &mut State| state.jd != jd) {
+            return Err(Error::ValueError(
+                "Epoch JDs do not match expected, this is only allowed if there is an associated FOV."
+                    .into(),
+            ));
         };
         Ok(SimultaneousStates {
             states,