[serve] split test_proxy.py into unit and e2e tests

[zcin]

Why are these changes needed?

Split out TestHTTPProxy and TestgRPCProxy into a unit test file.

pytest -vs python/ray/serve/tests/unit/test_proxy.py                                                                                                                                                                                                                       ─╯
2024-08-13 11:35:28,759 WARNING api.py:346 -- The default value for `max_ongoing_requests` has changed from 100 to 5 in Ray 2.32.0.
2024-08-13 11:35:28,759 WARNING api.py:397 -- The default value for `max_ongoing_requests` has changed from 100 to 5 in Ray 2.32.0.
============================================================================================================================= test session starts ==============================================================================================================================
platform darwin -- Python 3.9.12, pytest-7.4.0, pluggy-1.2.0 -- /Users/cindyz/miniforge3/envs/ray/bin/python
cachedir: .pytest_cache
rootdir: /Users/cindyz/ray
configfile: pytest.ini
plugins: docker-tools-3.1.3, asyncio-0.21.1, anyio-3.7.1
asyncio: mode=strict
collected 26 items

python/ray/serve/tests/unit/test_proxy.py::TestgRPCProxy::test_not_found_response 2024-08-13 11:35:28,801       INFO proxy.py:461 --  STATUSCODE.NOT_FOUND 0.0ms
2024-08-13 11:35:28,802 INFO proxy.py:461 --  STATUSCODE.NOT_FOUND 0.0ms
PASSED
...

============================================================================================================================== 26 passed in 0.05s ==============================================================================================================================

Related issue number

Checks

• I've signed off every commit(by using the -s flag, i.e., git commit -s) in this PR.
• I've run scripts/format.sh to lint the changes in this PR.
• I've included any doc changes needed for https://docs.ray.io/en/master/.
  • I've added any new APIs to the API Reference. For example, if I added a
    method in Tune, I've added it in doc/source/tune/api/ under the
    corresponding .rst file.
• I've made sure the tests are passing. Note that there might be a few flaky tests, see the recent failures at https://flakey-tests.ray.io/
• Testing Strategy
  • Unit tests
  • Release tests
  • This PR is not tested :(

[GeneDer]

LGTM, just make sure to fix linting :)