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

gctrpc/rpc.swagger.json

@@ -2869,6 +2869,36 @@
         ]
       }
     },
+    "/v1/getopeninterest": {
+      "get": {
+        "operationId": "GoCryptoTraderService_GetOpenInterest",
+        "responses": {
+          "200": {
+            "description": "A successful response.",
+            "schema": {
+              "$ref": "#/definitions/gctrpcGetOpenInterestResponse"
+            }
+          },
+          "default": {
+            "description": "An unexpected error response.",
+            "schema": {
+              "$ref": "#/definitions/rpcStatus"
+            }
+          }
+        },
+        "parameters": [
+          {
+            "name": "exchange",
+            "in": "query",
+            "required": false,
+            "type": "string"
+          }
+        ],
+        "tags": [
+          "GoCryptoTraderService"
+        ]
+      }
+    },
     "/v1/getorder": {
       "post": {
         "operationId": "GoCryptoTraderService_GetOrder",
@@ -6291,6 +6321,18 @@
         }
       }
     },
+    "gctrpcGetOpenInterestResponse": {
+      "type": "object",
+      "properties": {
+        "data": {
+          "type": "array",
+          "items": {
+            "type": "object",
+            "$ref": "#/definitions/gctrpcOpenInterestDataResponse"
+          }
+        }
+      }
+    },
     "gctrpcGetOrderRequest": {
       "type": "object",
       "properties": {
@@ -6730,6 +6772,35 @@
         }
       }
     },
+    "gctrpcOpenInterestDataRequest": {
+      "type": "object",
+      "properties": {
+        "asset": {
+          "type": "string"
+        },
+        "pair": {
+          "$ref": "#/definitions/gctrpcCurrencyPair"
+        }
+      }
+    },
+    "gctrpcOpenInterestDataResponse": {
+      "type": "object",
+      "properties": {
+        "exchange": {
+          "type": "string"
+        },
+        "asset": {
+          "type": "string"
+        },
+        "pair": {
+          "$ref": "#/definitions/gctrpcCurrencyPair"
+        },
+        "openInterest": {
+          "type": "number",
+          "format": "double"
+        }
+      }
+    },
     "gctrpcOrderDetails": {
       "type": "object",
       "properties": {