Add SCPI parser tests

Comprehensive test suite for SCPI command parsing:
- SCPICommand dataclass tests (creation, keyword property)
- Parser tests for queries, commands, arguments
- IEEE 488.2 common command tests (*IDN?, *RST, etc.)
- Edge cases (whitespace, empty strings)
- Instrument-specific command tests

Also fixed bug where is_query was determined from command string
ending rather than header ending (handles queries with arguments).

src/py_dvt_ate/instruments/scpi.py

@@ -67,8 +67,6 @@ class SCPIParser:
         if not command_string:
             return SCPICommand(header="", arguments=[], is_query=False)
 
-        is_query = command_string.endswith("?")
-
         # Split into header and arguments on first whitespace
         parts = command_string.split(None, 1)
         header = parts[0]
@@ -79,6 +77,9 @@ class SCPIParser:
             arg_string = parts[1]
             arguments = [arg.strip() for arg in arg_string.split(",")]
 
+        # Query is determined by whether the header ends with '?'
+        is_query = header.endswith("?")
+
         return SCPICommand(
             header=header,
             arguments=arguments,