Fix handling of zero and empty cookie values in RequestsCookieJar

[egangi]

Description: This PR addresses a bug in the _find_no_duplicates method of RequestsCookieJar where cookies with values of 0 or empty strings ('') were not being returned correctly.

Changes included: Updated _find_no_duplicates to correctly return cookie values that are 0 or ''. Added and updated test cases in test_cookie.py to cover: -Cookies with value 0 -Cookies with empty string value -Cookies with None value -Cookies with domain and path matching -Overwriting cookies with zero values -Persistence of zero values after update

These changes ensure that the get method and other functions depending on _find_no_duplicates behave correctly for all valid cookie values.

Impact: Existing code that relies on _find_no_duplicates returning cookie.value is preserved.