improve logic for the small excessive/spam withdraw fee

[0xbigz]

some ideas following up on discord discussion around the withdraw fee logic:

https://discord.com/channels/849494028176588802/878700556904980500/1133953891306844201
https://discord.com/channels/849494028176588802/878700556904980500/1135670638368018552

some comments mentioned how its circumventable and too dependent on lifetime actions of the user account rather than spam over a window of time.

i suggest using last_active_slot to determine if the fee is warranted. maybe 30 slots or so? other projects that want to do yield aggregations have mentioned they want to rebalance every 1 minute or so without concerns