fix: Accept numeric-only Machine ID in Mabtech APEX parser

Some APEX instruments export only a numeric serial number (e.g. "554")
in the Machine ID field instead of the expected "Model Number" format
(e.g. "IRIS 1234"). This caused parsing to fail with
"Unable to interpret Machine ID".

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: nathan-stender

src/allotropy/parsers/mabtech_apex/mabtech_apex_structure.py

@@ -13,7 +13,7 @@
     Metadata,
     ProcessedData,
 )
-from allotropy.exceptions import AllotropeParsingError
+from allotropy.exceptions import AllotropeConversionError, AllotropeParsingError
 from allotropy.parsers.constants import NOT_APPLICABLE
 from allotropy.parsers.mabtech_apex import constants
 from allotropy.parsers.utils.pandas import SeriesData
@@ -22,20 +22,25 @@
 
 
 def create_metadata(plate_info: SeriesData, file_path: str) -> Metadata:
-    machine_id = assert_not_none(
-        re.match(
-            "([A-Z]+[a-z]*) ([0-9]+)",
-            plate_info[str, "Machine ID"],
-        ),
-        msg="Unable to interpret Machine ID",
-    )
+    raw_machine_id = plate_info[str, "Machine ID"]
+    machine_id_match = re.match(r"([A-Z]+[a-z]*) ([0-9]+)", raw_machine_id)
+
+    if machine_id_match:
+        model_number = machine_id_match.group(1)
+        serial_number = machine_id_match.group(2)
+    elif re.fullmatch(r"[0-9]+", raw_machine_id):
+        model_number = NOT_APPLICABLE
+        serial_number = raw_machine_id
+    else:
+        msg = f"Unable to interpret Machine ID: {raw_machine_id}"
+        raise AllotropeConversionError(msg)
 
     return Metadata(
         device_identifier=NOT_APPLICABLE,
         software_name=constants.SOFTWARE_NAME,
         software_version=plate_info.get(str, "Software Version"),
-        model_number=machine_id.group(1),
-        equipment_serial_number=machine_id.group(2),
+        model_number=model_number,
+        equipment_serial_number=serial_number,
         file_name=Path(file_path).name,
         unc_path=plate_info.get(str, "Path", file_path),
         custom_info=plate_info.get_unread(),