fix: resolve CLI solver state dimension mismatch

Removed mathematical singularity in HeatExchanger models (q_hot - q_cold = 0 was redundant) causing them to incorrectly request 3 equations without internal variables. Fixed ScrewEconomizerCompressor internal_state_len to perfectly align with the solver dimensions.

crates/components/src/heat_exchanger/bphx_exchanger.rs

@@ -89,6 +89,7 @@ impl BphxExchanger {
     ///
     /// ```
     /// use entropyk_components::heat_exchanger::{BphxExchanger, BphxGeometry};
+    /// use entropyk_components::Component;
     ///
     /// let geo = BphxGeometry::from_dh_area(0.003, 0.5, 20);
     /// let hx = BphxExchanger::new(geo);
@@ -171,6 +172,11 @@ impl BphxExchanger {
         &self.geometry
     }
 
+    /// Returns the name of the configured heat transfer correlation.
+    pub fn correlation_name(&self) -> &'static str {
+        self.correlation_selector.correlation.name()
+    }
+
     /// Returns the effective UA value (W/K).
     pub fn ua(&self) -> f64 {
         self.inner.ua()
@@ -401,7 +407,7 @@ mod tests {
     fn test_bphx_exchanger_creation() {
         let geo = test_geometry();
         let hx = BphxExchanger::new(geo);
-        assert_eq!(hx.n_equations(), 3);
+        assert_eq!(hx.n_equations(), 2);
         assert!(hx.ua() > 0.0);
     }