Return response objects from all client methods

[hownowstephen]

Summary

• send_request() now returns the requests.Response object instead of response.text
• Track API methods (identify, track, pageview, backfill, delete, add_device, delete_device, suppress, unsuppress, merge_customers) now return the response instead of None
• APIClient methods (send_email, send_push, etc.) continue to return parsed JSON dicts — switched from json.loads(resp) to resp.json()

Breaking change

Track API methods previously returned None. Code that checked result is None or relied on the falsy return will need updating. However, the most common usage pattern (cio.identify(...) without capturing return) is unaffected.

Example

# Before: no way to inspect the response
cio.identify(id="123", name="Alice")

# After: response available if needed
resp = cio.identify(id="123", name="Alice")
print(resp.status_code)  # 200

Closes #85

Test plan

• Updated test_client_base.py assertions for Response objects
• All existing Track API tests pass (use hooks, don't assert return values)
• All existing APIClient tests pass (return value contract unchanged — still dicts)
• Full test suite passes (28 tests)
• Lint passes

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Note

Medium Risk
This is a user-visible return-type change for ClientBase.send_request and all Track API calls, which can break callers that relied on None/string responses; runtime behavior otherwise stays the same.

Overview
Changes client return contracts to expose HTTP responses. ClientBase.send_request() now returns the full requests.Response object (instead of response.text), and all Track API methods (e.g. identify, track, delete, merge_customers) now return that response rather than None.

Keeps App API methods returning parsed JSON. APIClient transactional send methods switch from json.loads(resp) to resp.json() to match the new response type. Tests are updated to assert on status_code and response objects rather than raw strings.

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