allow cachebox 6

[braingram]

Closes #601

I saw no usage of API mentioned in the breaking changes for cachebox 6: https://github.com/awolverp/cachebox/releases/tag/v6.0.0

Testing locally with python 3.14 the tests passed except for one:

_______________________________________________________________________________________ TestPicklingSecurity.test_restricted_unpickler_memory_exhaustion_cve ________________________________________________________________________________________

self = <tests.test_serialization.TestPicklingSecurity object at 0x10ba28690>

    @pytest.mark.skipif(sys.platform == "win32", reason="Resource module is Unix-only")
    def test_restricted_unpickler_memory_exhaustion_cve(self):
        """CVE-2026-33155: Prevent DoS via massive allocation through REDUCE opcode.

        The payload calls bytes(10_000_000_000) which is allowed by find_class
        but would allocate ~9.3GB of memory. The fix should reject this before
        the allocation happens.
        """
        import resource

        # 1. Cap memory to 500MB to prevent system freezes during the test
        soft, hard = resource.getrlimit(resource.RLIMIT_AS)
        maxsize_bytes = 500 * 1024 * 1024
>       resource.setrlimit(resource.RLIMIT_AS, (maxsize_bytes, hard))
E       ValueError: current limit exceeds maximum limit

tests/test_serialization.py:241: ValueError

which I suspect is unrelated (and due to the system used for testing).

I wasn't able to run the test suite on python 3.15 since several test/static/dev dependencies (based on the current pins) don't have python 3.15 wheels. However with the changes in this PR I'm able to install deepdiff on python 3.15.