fix(gateway): address SonarQube PR-mode findings on F2/F3 code

- data_sink.py: _IDENTIFIER_RE uses \w+/re.ASCII instead of the
  equivalent-but-verbose [A-Za-z0-9_]+ character class (verified same
  match behavior). NOSONAR on update_write_status's 'async with no
  await inside' - deliberate, per the ponytail comment already in the
  method body (uniform async interface across DataSink, no async pg driver).
- test_grpc_server.py: move make_request() out of the pytest.raises
  block so exactly one call can raise the expected exception.
- sonar-project.properties: exclude ingestor/proto/ (generated grpc
  code) from analysis - its ReadTag/etc. names are dictated by
  grpcio-tools, not a style choice, and renaming them breaks the wire.

sonar-project.properties

@@ -8,3 +8,7 @@ sonar.python.coverage.reportPaths=coverage.xml
 sonar.python.xunit.reportPath=pytest.xml
 sonar.python.version=3.11
 sonar.coverage.exclusions=ingestor/app.py
+# Generated protoc/grpcio-tools output - not hand-maintained; renaming its
+# ReadTag/etc. methods to satisfy naming-convention rules would break gRPC
+# wire compatibility (grpcio-tools dictates these names, not style choice).
+sonar.exclusions=ingestor/proto/**