Epoch Island security record

For easiness of application development, it is helpful to have the most important information emitted by events at crucial state changes. The following informational content of events could be improved upon: 1. No event is emitted when `lpPositions` is deleted in L94. 1. The `Remove` event only contains the `positionId` which may lead to more complex information querying, especially when the value at that index was deleted. Consider adding the following parameters: `_upsideTokenAmount` and `_downsideTokenAmount`.

We have observed some incidents of undocumented behavior that the user should be informed about: 1. The fee mechanism is undocumented and users are currently not informed how the fee changes over time. 1. While it makes sense, the documentation does not reflect that users will not receive any fees back when calling `untake()`. 1. While some NatSpec inline code documentation is provided, they do not describe function parameters and return values. Consider adding these, at least for all publicly and externally callable functions.

We identified some code sections where gas usage could be improved: 1. `Vepoch.sol#L156` and `L160`: Consider caching the return value of the call to `calculateVeTokens(_tokenAmount, _duration)` in a new local variable and re-using it instead of having two calls. 1. `deposits` is currently a mapping. As it is used with a strictly incrementing index, an array can also be used. Storing new values in an array is cheaper than in a mapping.

In `withdrawForfeit()`, the deposit is never deleted even when `percentage` is 100%. So an attacker could call `withdrawForfeit()` multiple times and pass in engineered numbers of `_depositTokensToRemove` to deliberately introduce rounding errors that allow the contract to return all of the deposited tokens while keeping some dust `rewardStakingPower` inside the contract. If this happens, the attacker can be rewarded without keeping any deposits in the contract.