fix: :bug: FastAPICache.clear | do not hardcode namespace if a key is provided

[thentgesMindee]

Hi again! Following my previous PR #72

Here is a fix we need to avoid breaking the inmemory and redis backends.

Explanation

both InMemoryBackend and RedisBackend clear methods have the following code:

if namespace:
    do_something()
elif key:
    do_something_else()

My last fix, since it was always setting a value for namespace was breaking the case namespace is None and key is not None since it would NEVER go to the elif key.

Testing

again, no test suite being configured, I had to manually test it. Here is a (dirty) testing file you can use, feel free to add it to your test suite when adding tests.

def clear(namespace=None, key=None):
    prefix = "prefix"
    if key is None or namespace is not None:
        namespace = prefix + (":" + namespace if namespace else "")
    return namespace, key


res = clear()
assert res == ("prefix", None), res

res = clear(namespace="mock")
assert res == ("prefix:mock", None), res

res = clear(key="mock")
assert clear(key="mock") == (None, "mock"), res

res = clear(namespace="mock", key="mock")
assert res == ("prefix:mock", "mock"), res