Fix CachedResposnse.read() and ClientResponse.read() consistency

[alessio-locatelli]

Closes #289

Inconsistency

• ClientResponse allows to call read() multiple times, returning a full content.

• CachedResponse allows to call read() multiple times, but silently returns nothing on further calls.

@JWCook Would you mind sharing your viewpoint? If this behavior is intentional, I will update the test accordingly.

---

UPDATE 2024-10-30:
I do not know if anyone ever calls read() more than once, so you may want to keep this change unreleased for a while or create a pre-release.

[JWCook]

You're correct. I must have done it that way because that's how streaming responses behave in requests, but we should make this consistent with aiohttp. Thanks.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.17%. Comparing base (fb00280) to head (ffbd394).
Report is 4 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #279   +/-   ##
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  Coverage   96.17%   96.17%           
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  Files          10       10           
  Lines        1072     1072           
  Branches      188      188           
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  Hits         1031     1031           
  Misses         30       30           
  Partials       11       11           

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