refactor: remove @dqbd/tiktoken dependency

chore(tsconfig.json): change target to ESNext
The @dqbd/tiktoken dependency was removed from the package.json file. This dependency was not being used in the project and was therefore removed to reduce the size of the project. The target in the tsconfig.json file was changed from ES2020 to ESNext to allow for the use of the latest ECMAScript features.

package.json

@@ -60,7 +60,6 @@
   },
   "dependencies": {
     "@clack/prompts": "^0.6.1",
-    "@dqbd/tiktoken": "^1.0.2",
     "axios": "^1.3.4",
     "chalk": "^5.2.0",
     "cleye": "^1.3.2",

tsconfig.json

@@ -1,6 +1,6 @@
 {
   "compilerOptions": {
-    "target": "ES2020",
+    "target": "ESNext",
     "lib": ["ES5", "ES6"],
 
     "module": "ESNext",