Function validateSignal

Validates ISignalDto returned by getSignal, branching on the same logic as ClientStrategy GET_SIGNAL_FN.

When priceOpen is provided:

• If currentPrice already reached priceOpen (shouldActivateImmediately) → validates as pending: currentPrice must be between SL and TP
• Otherwise → validates as scheduled: priceOpen must be between SL and TP

When priceOpen is absent:

• Validates as pending: currentPrice must be between SL and TP

Checks:

• currentPrice is a finite positive number
• Common signal fields via validateCommonSignal (position, prices, TP/SL relationships, minuteEstimatedTime)
• Position-specific immediate-close protection (pending) or activation-close protection (scheduled)