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/vendors/data/swep/bphx/B8THx30.json

@@ -0,0 +1,9 @@
+{
+    "model": "B8THx30",
+    "manufacturer": "SWEP",
+    "num_plates": 30,
+    "area": 0.72,
+    "dh": 0.0025,
+    "chevron_angle": 60.0,
+    "ua_nominal": 2500.0
+}