FIX forward mmap_mode to store backend in MemorizedResult - #1799

MemorizedResult takes an mmap_mode argument but never passes it to its store backend. _store_backend_factory is called without backend_options, so the backend keeps mmap_mode=None and load_item loads arrays fully into memory even when mmap_mode="r" was requested. MemorizedFunc already forwards it the same way (via backend_options).

So reconstructing a cached result from a location and asking for mmap gives you a plain array instead of a memmap:

cached = f.call_and_shelve()
direct = MemorizedResult(cached.store_backend.location, cached._call_id, mmap_mode="r")
direct.store_backend.mmap_mode   # None, should be "r"
type(direct.get())               # ndarray, should be memmap

The fix forwards mmap_mode to the factory, matching MemorizedFunc. Added a regression test. Full test_memory.py passes (68), ruff clean.