cleanup: pagination tests

[dbolduc]

The gaxi pagination tests use a custom Client, which will not stay in step with our generated code.

google-cloud-rust/src/gax-internal/tests/paginator.rs

Lines 108 to 122 in 1b2652c

	pub fn list_stream(
	&self,
	req: ListFoosRequest,
	) -> Paginator<ListFoosResponse, gax::error::Error> {
	let inner = self.inner.clone();
	let execute = move |page_token| {
	let mut request = req.clone();
	request.page_token = page_token;
	let client = Self {
	inner: inner.clone(),
	};
	client.list_impl(request)
	};
	Paginator::new(String::new(), execute)
	}

We would rather use a real client. While we could send real requests to a fake server at some local endpoint, it seems even better to just stub out the transport.

Add direct tests for the Paginator, in addition to the tests for the ItemPaginator.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.18%. Comparing base (1b2652c) to head (d42c14f).
Report is 6 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1703      +/-   ##
==========================================
- Coverage   96.23%   96.18%   -0.05%     
==========================================
  Files          49       48       -1     
  Lines        1857     1809      -48     
==========================================
- Hits         1787     1740      -47     
+ Misses         70       69       -1     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.