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

backtester/common/common_test.go

@@ -142,7 +142,7 @@ func TestDataTypeConversion(t *testing.T) {
 
 func TestFitStringToLimit(t *testing.T) {
 	t.Parallel()
-	for _, ti := range []struct {
+	for _, tc := range []struct {
 		str      string
 		sep      string
 		limit    int
@@ -187,13 +187,9 @@ func TestFitStringToLimit(t *testing.T) {
 			expected: "h",
 		},
 	} {
-		test := ti
-		t.Run(test.str, func(t *testing.T) {
+		t.Run(tc.str, func(t *testing.T) {
 			t.Parallel()
-			result := FitStringToLimit(test.str, test.sep, test.limit, test.upper)
-			if result != test.expected {
-				t.Errorf("received '%v' expected '%v'", result, test.expected)
-			}
+			assert.Equal(t, tc.expected, FitStringToLimit(tc.str, tc.sep, tc.limit, tc.upper))
 		})
 	}
 }