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/coinut/coinut.go

@@ -3,6 +3,7 @@ package coinut
 import (
 	"bytes"
 	"context"
+	"encoding/hex"
 	"errors"
 	"fmt"
 	"math/rand"
@@ -291,7 +292,7 @@ func (c *COINUT) SendHTTPRequest(ctx context.Context, ep exchange.URL, apiReques
 			if err != nil {
 				return nil, err
 			}
-			headers["X-SIGNATURE"] = crypto.HexEncodeToString(hmac)
+			headers["X-SIGNATURE"] = hex.EncodeToString(hmac)
 		}
 		headers["Content-Type"] = "application/json"
 

exchanges/coinut/coinut_websocket.go

@@ -2,6 +2,7 @@ package coinut
 
 import (
 	"context"
+	"encoding/hex"
 	"errors"
 	"fmt"
 	"net/http"
@@ -688,7 +689,7 @@ func (c *COINUT) wsAuthenticate(ctx context.Context) error {
 	if err != nil {
 		return err
 	}
-	r.Hmac = crypto.HexEncodeToString(hmac)
+	r.Hmac = hex.EncodeToString(hmac)
 
 	resp, err := c.Websocket.Conn.SendMessageReturnResponse(context.TODO(), request.Unset, r.Nonce, r)
 	if err != nil {