improve: [L08] Add comment about shutting down contract before uint32 timestamps roll over in year 2106

[nicholaspai]

Issue:

• [L08] Time is cast unsafely
  • In the HubPool function _updateAccumulatedLpFees, the return value of getCurrentTime() is cast to
    a uint32 value. This means that the value will be truncated to fit within 32 bits, and at some point
    around Feb 6, 2106, it will "roll over" and the value returned by casting to uint32 will drop down to 0.
    This will set pooledToken.lastLpFeeUpdate to a much lower number than the previous
    lastLpFeeUpdate. Any subsequent time _getAccumulatedFees is called, the
    timeFromLastInteraction calculation will be exceedingly high, and all "undistributed" fees will be
    accounted for as accumulated.
  • Again, note that this issue will only occur starting in the year 2106. Consider changing the size of the
    cast from uint32 to a larger number, like uint64. This should be more than enough to not encounter
    limits within a reasonably distant future. Alternatively, consider documenting the behavior and defining
    a procedure for what to do if the system is still in operation when the uint32 limit is hit, or for shutting
    down the system before the year 2106.

Solution:

• We use uint32 time-related variables to save gas costs by packing variables smartly, and we do intend to deprecate this contract by 2106. So we add a disclaimer at the top of the contract that it should be deprecated by 2106 and steps for doing so.

[mrice32]

LGTM!