fix(lint): remove unnecessary async keywords from synchronous functions

- Remove async from functions that don't use await
- Change return types from Promise<void> to void for synchronous functions
- Fixes all 8 require-await lint warnings
- Reduces total lint warnings from 63 to 55

ts/nupst.ts

@@ -130,7 +130,7 @@ export class Nupst {
    * Get the latest version from npm registry
    * @returns Promise resolving to the latest version string
    */
-  private async getLatestVersion(): Promise<string> {
+  private getLatestVersion(): Promise<string> {
     return new Promise<string>((resolve, reject) => {
       const options = {
         hostname: 'registry.npmjs.org',