bug: add operaton overflow

[xiaguan]

        Input {
            capacity: 16140894441656287227,
            cache_type: S3Fifo,
            operations: [
                Insert(
                    0,
                    15,
                    1085102592571150095,
                ),
                Insert(
                    15,
                    15,
                    18379149462045917184,
                ),
                Insert(
                    0,
                    0,
                    0,
                ),
            ],
        }

thread '<unnamed>' panicked at /home/susun/foyer/foyer-memory/src/generic.rs:229:15:
attempt to add with overflow

[MrCroxx]

Hi @xiaguan . Thanks for reporting it. IMO, providing an entry with a charge that causes usize overflow is not a bug. The user should guarantee that the charge is sound. And panic here is acceptable.