Some of our tests failed because RPC was canceled by server, error message:
```
I0000 00:00:1726598495.788119 64528 chttp2_transport.cc:1182] ipv4:127.0.0.1:41825: Got goaway [2] err=UNAVAILABLE:GOAWAY received; Error code: 2; Debug Text: Cancelling all calls {grpc_status:14, http2_error:2, created_time:"2024-09-17T18:41:35.78810597+00:00"}
```
It's possible that the request waited too long to be processed and thus canceled by server (default maximum time gRPC server allows a request to be received by the server but not handled is `30s`, controlled by `grpc.server_max_unrequested_time_in_server`).
This PR will print the test start/finish time so we know if we should increase `grpc.server_max_unrequested_time_in_server` time.
Example before change:
```
Testing gRPC Python...
SUCCESS tests.unit._metadata_flags_test.MetadataFlagsTest.test_call_wait_for_ready_default
Running tests.unit._metadata_flags_test.MetadataFlagsTest.test_call_wait_for_ready_disabled
SUCCESS tests.unit._metadata_flags_test.MetadataFlagsTest.test_call_wait_for_ready_disabled
Running tests.unit._metadata_flags_test.MetadataFlagsTest.test_call_wait_for_ready_enabled
```
Example after change:
```
[2024-09-20 18:32:15.228947]Testing gRPC Python...
[2024-09-20 18:32:15.237855]START tests.unit._metadata_flags_test.MetadataFlagsTest.test_call_wait_for_ready_default
[2024-09-20 18:32:15.265477]SUCCESS tests.unit._metadata_flags_test.MetadataFlagsTest.test_call_wait_for_ready_default[Duration: 0:00:00.027622s]
Running tests.unit._metadata_flags_test.MetadataFlagsTest.test_call_wait_for_ready_disabled
[2024-09-20 18:32:15.278142]START tests.unit._metadata_flags_test.MetadataFlagsTest.test_call_wait_for_ready_disabled
[2024-09-20 18:32:15.316065]FAILURE tests.unit._metadata_flags_test.MetadataFlagsTest.test_call_wait_for_ready_disabled[Duration: 0:00:00.037911]
Running tests.unit._metadata_flags_test.MetadataFlagsTest.test_call_wait_for_ready_enabled
[2024-09-20 18:32:15.328680]START tests.unit._metadata_flags_test.MetadataFlagsTest.test_call_wait_for_ready_enabled
[2024-09-20 18:32:16.938745]SUCCESS tests.unit._metadata_flags_test.MetadataFlagsTest.test_call_wait_for_ready_enabled[Duration: 0:00:01.610065s]
```
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Closes#37761
Xuan Wang
a9114ff9e4