Separate JBD decoding from serial transport

Move response decoding into jbd_proto and the data container into jbd_snapshot. Preserve the existing jbd_bms imports and test the transport boundary.

tests/test_backend_modules.py

@@ -20,6 +20,7 @@ COMPOSITE_TEMP_PACKET = (2, 0xFE, 0x15, b"\xb0\x06\x14")  # field 102: 20 C
 
 @pytest.mark.parametrize("first", [
     "ecoflow_proto", "ecoflow_river2", "ecoflow_river3", "ecoflow_snapshot",
+    "jbd_proto", "jbd_snapshot",
 ])
 def test_decoders_import_in_any_order_without_transport_dependencies(first):
     # A fresh interpreter catches import cycles hidden by pytest's import order.
@@ -37,8 +38,9 @@ class NoTransportImports(importlib.abc.MetaPathFinder):
 
 sys.meta_path.insert(0, NoTransportImports())
 importlib.import_module('bmspy.' + sys.argv[1])
-from bmspy import ecoflow_proto, ecoflow_river2, ecoflow_river3
+from bmspy import ecoflow_proto, ecoflow_river2, ecoflow_river3, jbd_proto
 from bmspy.ecoflow_snapshot import EcoFlowSnapshot
+from bmspy.jbd_snapshot import JBDBMS
 
 assert ecoflow_proto.format_payload(2, 0xFE, 0x15, b'\\x08\\x00') == [
     '[DisplayPropertyUpload]', '  errcode: 0',
@@ -46,7 +48,9 @@ assert ecoflow_proto.format_payload(2, 0xFE, 0x15, b'\\x08\\x00') == [
 assert ecoflow_proto.format_payload(2, 0x20, 2, bytes(23))[0] == '[PD heartbeat]'
 assert ecoflow_river2.decode_river2_payload(2, 0x20, 2, bytes(23))['soc'] == 0
 assert ecoflow_river3.decode_river3_payload(2, 0xFE, 0x15, b'\\x08\\x00') == {}
+assert jbd_proto.bytes_to_digits(1, 0) == 256
 assert list(EcoFlowSnapshot().items()) == []
+assert list(JBDBMS().items()) == []
 """
     result = subprocess.run(
         [sys.executable, "-c", script, first],
@@ -55,10 +59,17 @@ assert list(EcoFlowSnapshot().items()) == []
     assert result.returncode == 0, result.stderr
 
 
-def test_snapshot_and_decoder_imports_remain_compatible():
-    from bmspy import ecoflow_bt
+def test_snapshot_and_jbd_function_imports_remain_compatible():
+    from bmspy import ecoflow_bt, jbd_bms, jbd_proto
+    from bmspy.jbd_snapshot import JBDBMS
 
     assert ecoflow_bt.EcoFlowSnapshot is EcoFlowSnapshot
+    assert jbd_bms.JBDBMS is JBDBMS
+    for name in (
+        "bytes_to_digits", "bytes_to_date", "convert_to_signed",
+        "calculate_checksum", "verify_checksum", "parse_03_response", "parse_04_response",
+    ):
+        assert getattr(jbd_bms, name) is getattr(jbd_proto, name)
     assert ecoflow_bt.decode_river2_payload is ecoflow_river2.decode_river2_payload
     assert ecoflow_bt.decode_river3_payload is ecoflow_river3.decode_river3_payload