Added NI TestStand code to example measurements using NI gRPC Device remoting (#151)

* Makes instrument type ids more discoverable
  * Adds constants for instrument_type_id to session_management module
  * Updates examples to use INSTRUMENT_TYPE_ constants

* Adds NI TestStand code to example measurements that use NI gRPC Device remoting
  * Copies `_helpers.py`, `teststand_fixture.py`, and `NIDCPowerSourceDCVoltage.seq` from NI-DCPower example to other examples
  * Updates `teststand_fixture.py` and sequence files to work with respective examples

Author: tkrebes

examples/nidcpower_source_dc_voltage/NIDCPowerSourceDCVoltage.seq

@@ -65,7 +65,7 @@ def measure(
             session_management_client.reserve_sessions(
                 context=measurement_service.context.pin_map_context,
                 pin_names=[pin_name],
-                instrument_type_id="niDCPower",
+                instrument_type_id=nims.session_management.INSTRUMENT_TYPE_NI_DCPOWER,
                 timeout=-1,
             )
         )

examples/nidcpower_source_dc_voltage/measurement.py

@@ -32,7 +32,7 @@ def create_nidcpower_sessions(pin_map_id: str):
         pin_map_context = nims.session_management.PinMapContext(pin_map_id=pin_map_id, sites=None)
         with session_management_client.reserve_sessions(
             context=pin_map_context,
-            instrument_type_id="niDCPower",
+            instrument_type_id=nims.session_management.INSTRUMENT_TYPE_NI_DCPOWER,
             timeout=-1,
         ) as reservation:
 
@@ -64,7 +64,8 @@ def destroy_nidcpower_sessions():
             nidcpower_sessions = [
                 session_info
                 for session_info in reservation.session_info
-                if session_info.instrument_type_id == "niDCPower"
+                if session_info.instrument_type_id
+                == nims.session_management.INSTRUMENT_TYPE_NI_DCPOWER
             ]
 
             session_management_client.unregister_sessions(nidcpower_sessions)