Add support for redis functions (#2020)

* fix #1906 - implement BITFIELD_RO

* initial support for redis functions

* fix test utils

* redis functions commands and tests

* upgrade deps

* fix "Property 'uninstall' does not exist on type 'SinonFakeTimers'"

* upgrade dockers version

* Merge branch 'master' of github.com:redis/node-redis into functions

* fix FUNCTION LIST WITHCODE and FUNCTION STATS

* upgrade deps

* set minimum version for FCALL and FCALL_RO

* fix FUNCTION LOAD

* FUNCTION LOAD

* fix FUNCTION LOAD & FUNCTION LIST & FUNCTION LOAD WITHCODE

* fix FUNCTION_LIST_WITHCODE test

packages/client/lib/commands/FUNCTION_STATS.ts

@@ -0,0 +1,56 @@
+import { RedisCommandArguments } from '.';
+
+export function transformArguments(): RedisCommandArguments {
+    return ['FUNCTION', 'STATS'];
+}
+
+type FunctionStatsRawReply = [
+    'running_script',
+    null | [
+        'name',
+        string,
+        'command',
+        string,
+        'duration_ms',
+        number
+    ],
+    'engines',
+    Array<any> // "flat tuples" (there is no way to type that)
+    // ...[string, [
+    //     'libraries_count',
+    //     number,
+    //     'functions_count',
+    //     number
+    // ]]
+];
+
+interface FunctionStatsReply {
+    runningScript: null | {
+        name: string;
+        command: string;
+        durationMs: number;
+    };
+    engines: Record<string, {
+        librariesCount: number;
+        functionsCount: number;
+    }>;
+}
+
+export function transformReply(reply: FunctionStatsRawReply): FunctionStatsReply {
+    const engines = Object.create(null);
+    for (let i = 0; i < reply[3].length; i++) {
+        engines[reply[3][i]] = {
+            librariesCount: reply[3][++i][1],
+            functionsCount: reply[3][i][3]
+        };
+    }
+
+    return {
+        runningScript: reply[1] === null ? null : {
+            name: reply[1][1],
+            command: reply[1][3],
+            durationMs: reply[1][5]
+        },
+        engines
+    };
+}