Fix make test-interop errors

[gophergogo]

This is the follow-up work of #270

[==========] Running 6 tests from 1 test suite.
[----------] Global test environment set-up.
[----------] 6 tests from OfficialServerInteropTest
[ DISABLED ] OfficialServerInteropTest.DISABLED_TheHandshakeIsAnsweredAndUnderstood
[ RUN      ] OfficialServerInteropTest.AToolIsCalledAndAnswersExactly
/Users/ganan/ws/mcpws/gopher-mcp/tests/interop/test_client_vs_official_server.cc:319: Failure
Value of: server_.start()
  Actual: false
Expected: true
[  FAILED  ] OfficialServerInteropTest.AToolIsCalledAndAnswersExactly (10064 ms)
[ RUN      ] OfficialServerInteropTest.ProgressArrivesBeforeTheAnswer
/Users/ganan/ws/mcpws/gopher-mcp/tests/interop/test_client_vs_official_server.cc:337: Failure
Value of: server_.start()
  Actual: false
Expected: true
[  FAILED  ] OfficialServerInteropTest.ProgressArrivesBeforeTheAnswer (10034 ms)
[ RUN      ] OfficialServerInteropTest.APushArrivesOnTheHeldStream
/Users/ganan/ws/mcpws/gopher-mcp/tests/interop/test_client_vs_official_server.cc:365: Failure
Value of: server_.start()
  Actual: false
Expected: true
[  FAILED  ] OfficialServerInteropTest.APushArrivesOnTheHeldStream (10010 ms)
[ DISABLED ] OfficialServerInteropTest.DISABLED_AQuestionFromTheServerIsAnswered
[ RUN      ] OfficialServerInteropTest.AResourceAndAPromptAreReadExactly
/Users/ganan/ws/mcpws/gopher-mcp/tests/interop/test_client_vs_official_server.cc:405: Failure
Value of: server_.start()
  Actual: false
Expected: true
[  FAILED  ] OfficialServerInteropTest.AResourceAndAPromptAreReadExactly (10041 ms)
[ RUN      ] OfficialServerInteropTest.AServerKeepingNoSessionsStillWorks
/Users/ganan/ws/mcpws/gopher-mcp/tests/interop/test_client_vs_official_server.cc:433: Failure
Value of: server_.start({"--stateless"})
  Actual: false
Expected: true
[  FAILED  ] OfficialServerInteropTest.AServerKeepingNoSessionsStillWorks (10043 ms)
[ RUN      ] OfficialServerInteropTest.TheTransportIsWorkedOutByAsking
/Users/ganan/ws/mcpws/gopher-mcp/tests/interop/test_client_vs_official_server.cc:447: Failure
Value of: server_.start()
  Actual: false
Expected: true
[  FAILED  ] OfficialServerInteropTest.TheTransportIsWorkedOutByAsking (10009 ms)
[----------] 6 tests from OfficialServerInteropTest (60204 ms total)

[----------] Global test environment tear-down
[==========] 6 tests from 1 test suite ran. (60204 ms total)
[  PASSED  ] 0 tests.
[  FAILED  ] 6 tests, listed below:
[  FAILED  ] OfficialServerInteropTest.AToolIsCalledAndAnswersExactly
[  FAILED  ] OfficialServerInteropTest.ProgressArrivesBeforeTheAnswer
[  FAILED  ] OfficialServerInteropTest.APushArrivesOnTheHeldStream
[  FAILED  ] OfficialServerInteropTest.AResourceAndAPromptAreReadExactly
[  FAILED  ] OfficialServerInteropTest.AServerKeepingNoSessionsStillWorks
[  FAILED  ] OfficialServerInteropTest.TheTransportIsWorkedOutByAsking

 6 FAILED TESTS
  YOU HAVE 2 DISABLED TESTS

make: *** [test-interop] Error 1