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/protocol/features.go

@@ -46,7 +46,6 @@ type Features struct {
 	MultiChainDeposits                bool `json:"multiChainDeposits,omitempty"`
 	MultiChainWithdrawals             bool `json:"multiChainWithdrawals,omitempty"`
 	MultiChainDepositRequiresChainSet bool `json:"multiChainDepositRequiresChainSet,omitempty"`
-
 	// HasAssetTypeAccountSegregation is when the assets are divided into asset
 	// types instead of just being denoted as spot holdings.
 	HasAssetTypeAccountSegregation bool `json:"hasAssetTypeAccountSegregation,omitempty"`