chore: add event to dsf reset on full withdrawal

[eigenmikem]

Motivation:

DSF reset isn't emitting event on a full withdrawal.

Modifications:

Added event and shadowed declaration to resolve stack too deep

Result:

Easier for front-end to track dsf changes.

[ypatil12]

If I do this:

            if (sharesAfter == 0) {
                DepositScalingFactor storage _dsf = _depositScalingFactor[staker][strategies[i]];
                _dsf.reset();
                emit DepositScalingFactorUpdated(staker, strategies[i], _dsf.scalingFactor());
            }

I don't get a stack too deep

[wadealexc]

LGTM. Agree with Yash, but IMO it's a bit cleaner to just use a storage pointer at the top of the method.