feat: add MCU communication support to write filter coefficients via serial port

tests/test_dea_api.py

@@ -9,11 +9,13 @@ from dea_api import (
     BodeCompareParams,
     BodeParams,
     DesignParams,
+    MCUWriteParams,
     add_security_headers,
     calculate_bode,
     calculate_bode_compare,
     design_filter,
     filter_csv,
+    write_mcu_command,
 )
 
 
@@ -86,6 +88,15 @@ class DeaApiTest(unittest.TestCase):
         self.assertEqual(len(body["freq"]), len(body["fixed"]["mag"]))
         self.assertEqual(len(body["ideal"]["phase"]), len(body["fixed"]["phase"]))
 
+    def test_mcu_write_rejects_invalid_command_format(self):
+        try:
+            write_mcu_command(MCUWriteParams(command="hello"))
+        except HTTPException as exc:
+            self.assertEqual(exc.status_code, 400)
+            self.assertIn("MCU", exc.detail)
+        else:
+            raise AssertionError("Expected invalid MCU command validation to fail")
+
 
     def test_filter_downsamples_plot_response_for_large_csv(self):
         rows = ["value"] + [str(i) for i in range(6001)]