get Actual Capacity
Gets the absolute maximum number of items the filter can theoretically hold. This is NOT the maximum you can expect it to reliably hold. This should only be used if you understand the source. Internal restrictions on backing array size and compensation for the expected filter occupancy on first insert failure nearly always make the filter larger than requested on creation. This method returns how big the filter actually is (in items) DO NOT EXPECT IT TO BE ABLE TO HOLD THIS MANY
Return
number of keys filter can theoretically hold at 100% fill