fix(client): type fixes

[sauyon]

Depends on #4181.

Review the second commit if you want to review this now.

[pep8speaks]

Hello @sauyon! Thanks for updating this PR. We checked the lines you've touched for PEP 8 issues, and found:

• In the file src/bentoml/_internal/client/__init__.py:

Line 85:80: E501 line too long (85 > 79 characters)

• In the file tests/e2e/bento_server_http/tests/test_serve.py:

Line 47:80: E501 line too long (93 > 79 characters)
Line 80:80: E501 line too long (93 > 79 characters)
Line 111:80: E501 line too long (93 > 79 characters)
Line 141:80: E501 line too long (81 > 79 characters)
Line 142:80: E501 line too long (81 > 79 characters)
Line 146:80: E501 line too long (80 > 79 characters)