Fix tests using global_config.update

[dimos-bot]

Now that global_config is a global singleton, calling global_config.update updates the values for all the subsequent tests. We need to reset to the original values after each test. Note that using blueprint.global_config also modifies the global singleton so it's not an alternative.

dimos/core/tests/e2e_mcp_killtest.py:96:    global_config.update(viewer_backend="none", n_workers=1)
dimos/core/blueprints.py:501:        global_config.update(**dict(self.global_config_overrides))
dimos/core/blueprints.py:503:            global_config.update(**dict(cli_config_overrides))
dimos/core/test_e2e_daemon.py:83:    global_config.update(viewer_backend="none", n_workers=1)
dimos/core/test_e2e_daemon.py:93:    global_config.update(viewer_backend="none", n_workers=2)
dimos/core/test_e2e_daemon.py:228:    global_config.update(viewer_backend="none", n_workers=1)
dimos/core/test_e2e_mcp_stress.py:64:    global_config.update(viewer_backend="none", n_workers=1)
dimos/core/test_e2e_mcp_stress.py:215:        global_config.update(viewer_backend="none", n_workers=1)
dimos/core/test_e2e_mcp_stress.py:230:        global_config.update(viewer_backend="none", n_workers=1)
dimos/core/test_e2e_mcp_stress.py:409:        global_config.update(viewer_backend="none", n_workers=1)
dimos/robot/cli/dimos.py:127:    global_config.update(**cli_config_overrides)
dimos/robot/cli/dimos.py:411:    global_config.update(**cli_config_overrides)
dimos/agents/conftest.py:81:        global_config.update(viewer_backend="none")
dimos/agents/mcp/conftest.py:80:        global_config.update(viewer_backend="none")

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Synced from DIM-697