Fix: responses/__init__.py's _on_request() (~line 1099) mutated the SAME...

[M001N]

Summary

In _on_request(), params/req_kwargs are still set on request before calling _find_match() (needed because matchers.py's query_param_matcher/request_kwargs_matcher read them during matching). Immediately after matching completes, a shallow copy (call_request = copy.copy(request)) is taken to carry those attributes for the internal call log, and del request.params / del request.req_kwargs strips them from the live request object before it can flow onward to the caller (via response.request or a raised exception's .request). All Call(...)/self._calls.add(...) construction sites in _on_request were switched to use call_request instead of request, so responses.calls[i].request.params/.req_kwargs keep working exactly as documented. Updated README.rst's query-params example and two existing tests (test_matchers.py::test_request_matches_params and test_responses.py's assert_params helper used by test_request_param*) that had been asserting .params on the live resp.request object, to instead read it from responses.calls[...].request, since that behavior was the actual bug.

Problem

getsentry/responses issue reference: #738

Root Cause

responses/init.py's _on_request() (~line 1099) mutated the SAME live PreparedRequest instance that requests threads back to the caller (via response.request / exception.request) by doing request.params = ... and request.req_kwargs = kwargs directly on it. Since that mutation happened before matching and was never undone, these responses-internal attributes stayed attached to the request object visible to caller code (e.g. in a raised exception's .request), leaking mock-only internals into what should look like a plain, real PreparedRequest.

Testing

PASS - full suite: 231 passed, 0 failed (18 pre-existing unrelated deprecation warnings).

Related Issue

#738

[markstory]

This could break userland code. But I don't see how we fix the reported issue without removing this attribute.