exchanges/futures: Implement open interest (#1417)

* adds open interest to exchanges

* ADDS TESTING YEAH

* New endpoints, BTSE, RPCS, cached

* slight design change, begin gateio

You will need to get cached for
each exchange that supports it

* gateio, huobi, rpc

* fix up kraken, cache retrieval

* okx, gateio

* finalising all implementations and tests

* definitely my final ever commit on this

* Well, well, well

* final v2

* quick fix of bug

* test coverage, assert notempty, test helper

Added a new testhelper for currency
management because its very annoying
in a parallel test setting which wastes
so much space otherwise

* minimises REST requests for Open Interest

* types.Number merge misses

* Minimises Kraken REST calls

* len change, value -> pointer receiver

* further fixup

* fixes gateio, batch calculates open interest

* single gateio, lint const fixes

* rejig and more thorough oi for huobi

* formatting expansion

* minor fix for handling expiring contracts

* rm unused Binance strings

* add bybit support, fix bybit issues

* oopsie doopsie, dont look at my whoopsie

* Fix issue, remove feature

* move an irrelevant function for the pr

* mini bybit upgrades

* fixes cli request bug

exchanges/ticker/ticker.go

@@ -14,12 +14,16 @@ import (
 )
 
 var (
+	// ErrNoTickerFound is when a ticker is not found
+	ErrNoTickerFound = errors.New("no ticker found")
 	// ErrBidEqualsAsk error for locked markets
-	ErrBidEqualsAsk        = errors.New("bid equals ask this is a crossed or locked market")
+	ErrBidEqualsAsk = errors.New("bid equals ask this is a crossed or locked market")
+
 	errInvalidTicker       = errors.New("invalid ticker")
 	errTickerNotFound      = errors.New("ticker not found")
 	errExchangeNameIsEmpty = errors.New("exchange name is empty")
 	errBidGreaterThanAsk   = errors.New("bid greater than ask this is a crossed or locked market")
+	errExchangeNotFound    = errors.New("exchange not found")
 )
 
 func init() {
@@ -85,14 +89,41 @@ func GetTicker(exchange string, p currency.Pair, a asset.Item) (*Price, error) {
 		Asset:    a,
 	}]
 	if !ok {
-		return nil, fmt.Errorf("no tickers associated with asset type %s %s %s",
-			exchange, p, a)
+		return nil, fmt.Errorf("%w %s %s %s",
+			ErrNoTickerFound, exchange, p, a)
 	}
 
 	cpy := tick.Price // Don't let external functions have access to underlying
 	return &cpy, nil
 }
 
+// GetExchangeTickers returns all tickers for a given exchange
+func GetExchangeTickers(exchange string) ([]*Price, error) {
+	return service.getExchangeTickers(exchange)
+}
+
+func (s *Service) getExchangeTickers(exchange string) ([]*Price, error) {
+	if exchange == "" {
+		return nil, errExchangeNameIsEmpty
+	}
+	exchange = strings.ToLower(exchange)
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	_, ok := s.Exchange[exchange]
+	if !ok {
+		return nil, fmt.Errorf("%w %v", errExchangeNotFound, exchange)
+	}
+	tickers := make([]*Price, 0, len(s.Tickers))
+	for k, v := range s.Tickers {
+		if k.Exchange != exchange {
+			continue
+		}
+		cpy := v.Price // Don't let external functions have access to underlying
+		tickers = append(tickers, &cpy)
+	}
+	return tickers, nil
+}
+
 // FindLast searches for a currency pair and returns the first available
 func FindLast(p currency.Pair, a asset.Item) (float64, error) {
 	service.mu.Lock()
@@ -206,7 +237,7 @@ func (s *Service) setItemID(t *Ticker, p *Price, exch string) error {
 	return nil
 }
 
-// getAssociations links a singular book with it's dispatch associations
+// getAssociations links a singular book with its dispatch associations
 func (s *Service) getAssociations(exch string) ([]uuid.UUID, error) {
 	if exch == "" {
 		return nil, errExchangeNameIsEmpty