MISC: refactor weaken effect calculation (#1076)

so far we calculate the effect of weaken in three +1 places
ns.weaken
ns.weakenAnalyze
terminal weaken

and server.weaken where the bn mult is applied

i extracted the logic into a new netscript helper function getWeakenEffect
this gives us one place if we want to change the formula

a side effect i added the server.cpuCores to the terminal weaken to future proof it if the npc server core pr (#963) is merged

src/Server/Server.ts

@@ -141,7 +141,7 @@ export class Server extends BaseServer {
 
   /** Lowers the server's security level (difficulty) by the specified amount) */
   weaken(amt: number): void {
-    this.hackDifficulty -= amt * currentNodeMults.ServerWeakenRate;
+    this.hackDifficulty -= amt;
     this.capDifficulty();
   }
 

src/Server/ServerHelpers.ts

@@ -2,7 +2,7 @@ import { GetServer, createUniqueRandomIp, ipExists } from "./AllServers";
 import { Server, IConstructorParams } from "./Server";
 import { BaseServer } from "./BaseServer";
 import { calculateServerGrowth, calculateServerGrowthLog } from "./formulas/grow";
-
+import { currentNodeMults } from "../BitNode/BitNodeMultipliers";
 import { ServerConstants } from "./data/Constants";
 import { Player } from "@player";
 import { CompletedProgramName, LiteratureName } from "@enums";
@@ -258,3 +258,8 @@ export function getCoreBonus(cores = 1): number {
   const coreBonus = 1 + (cores - 1) / 16;
   return coreBonus;
 }
+
+export function getWeakenEffect(threads: number, cores: number): number {
+  const coreBonus = getCoreBonus(cores);
+  return ServerConstants.ServerWeakenAmount * threads * coreBonus * currentNodeMults.ServerWeakenRate;
+}