Optimize import loading time

[jrafkind-ai]

Please consider optimizing the imports that this library performs. On my system a single import vertexai takes about 1 second.

The top 3 modules that take the most time can be computed with -X importtime

$ python -X importtime -m vertexai &> x
$ sort -k 3 -n x | tail -n 3
import time:      7300 |       7300 |                         google.cloud.aiplatform_v1beta1.types.evaluation_service
import time:     53394 |      53394 |                         google.cloud.aiplatform_v1beta1.services.pipeline_service.transports.rest_asyncio
import time:    244048 |     259512 |       google.api_core

Where the numbers are measured in microseconds (us).

Version: google-cloud-aiplatform v1.128.0