codebase: Cleanup various things (#1935)

* codebase: Rid base64/hex to string common funcs

* codebase: Rid local scope variable usage and other improvements

* codebase: Refactor currency pair usage across multiple exchanges

- Updated HitBTC tests to use the new currency pair format.
- Modified Kraken futures types to use currency.Pair instead of string for Symbol.
- Adjusted Kraken wrapper methods to handle currency pairs correctly.
- Refined OKX tests and types to utilize currency.Pair for instrument IDs.
- Enhanced Poloniex tests to consistently use predefined currency pairs.
- Streamlined order and orderbook tests to replace string pairs with currency.NewBTCUSD().
- Improved Yobit tests to utilize a standardized currency pair format.
- Updated validator wrapper to use currency pairs directly instead of string conversions.

* codebase: Use types.Number where possible

* refactor: update PayoutFee type to types.Number for consistency

* Refactor: Remove crypto functions to use standard library and other minor changes

- Removed custom crypto functions for SHA256, SHA512, and MD5 from the common/crypto package.
- Replaced usages of removed functions with standard library implementations in various files including:
  - cmd/websocket_client/main.go
  - engine/apiserver.go
  - exchanges/kraken/kraken.go
  - exchanges/lbank/lbank.go
  - exchanges/okx/okx_business_websocket.go
  - exchanges/kucoin/kucoin_websocket.go
  - gctscript/vm/vm.go
- Updated tests to reflect changes in the crypto functions.
- Renamed several functions for clarity, particularly in the context of order book updates across multiple exchanges.

* refactor: replace assert with require for consistency in test assertions

* refactor: Improve Binance futures candlestick test, standardise orderbook update function names and improve test parallelism

* refactor: Replace require.Len with require.Equal for better output in TestGetFuturesKlineData

exchanges/bitstamp/bitstamp_wrapper.go

@@ -819,7 +819,7 @@ func (b *Bitstamp) GetHistoricCandles(ctx context.Context, pair currency.Pair, a
 
 	timeSeries := make([]kline.Candle, 0, len(candles.Data.OHLCV))
 	for x := range candles.Data.OHLCV {
-		timestamp := time.Unix(candles.Data.OHLCV[x].Timestamp, 0)
+		timestamp := candles.Data.OHLCV[x].Timestamp.Time()
 		if timestamp.Before(req.Start) || timestamp.After(req.End) {
 			continue
 		}
@@ -857,13 +857,13 @@ func (b *Bitstamp) GetHistoricCandlesExtended(ctx context.Context, pair currency
 		}
 
 		for i := range candles.Data.OHLCV {
-			timestamp := time.Unix(candles.Data.OHLCV[i].Timestamp, 0)
+			timestamp := candles.Data.OHLCV[i].Timestamp.Time()
 			if timestamp.Before(req.RangeHolder.Ranges[x].Start.Time) ||
 				timestamp.After(req.RangeHolder.Ranges[x].End.Time) {
 				continue
 			}
 			timeSeries = append(timeSeries, kline.Candle{
-				Time:   time.Unix(candles.Data.OHLCV[i].Timestamp, 0),
+				Time:   timestamp,
 				Open:   candles.Data.OHLCV[i].Open,
 				High:   candles.Data.OHLCV[i].High,
 				Low:    candles.Data.OHLCV[i].Low,