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/B5THx20.json

@@ -0,0 +1,41 @@
+{
+    "model": "B5THx20",
+    "manufacturer": "SWEP",
+    "num_plates": 20,
+    "area": 0.45,
+    "dh": 0.003,
+    "chevron_angle": 65.0,
+    "ua_nominal": 1500.0,
+    "ua_curve": {
+        "points": [
+            [
+                0.2,
+                0.30
+            ],
+            [
+                0.4,
+                0.55
+            ],
+            [
+                0.6,
+                0.72
+            ],
+            [
+                0.8,
+                0.88
+            ],
+            [
+                1.0,
+                1.00
+            ],
+            [
+                1.2,
+                1.08
+            ],
+            [
+                1.5,
+                1.15
+            ]
+        ]
+    }
+}

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
+}

crates/vendors/data/swep/bphx/index.json

@@ -0,0 +1,4 @@
+[
+    "B5THx20",
+    "B8THx30"
+]