fix: Use dynamic imports in d.ts file

ftp-srv.d.ts

@@ -1,6 +1,4 @@
-import * as tls from 'tls'
-import { Stats } from 'fs'
-import { EventEmitter } from 'events'
+const EventEmitter = import('events').EventEmitter
 
 export class FileSystem {
   readonly connection: FtpConnection
@@ -112,11 +110,11 @@ export interface FtpServerOptions {
   pasv_url?: string
   random_pasv_port?: boolean
   greeting?: string | string[]
-  tls?: tls.SecureContextOptions | false
+  tls?: import('tls').SecureContextOptions | false
   anonymous?: boolean
   blacklist?: Array<string>
   whitelist?: Array<string>
-  file_format?: (stat: Stats) => string | Promise<string> | 'ls' | 'ep'
+  file_format?: ((stat: import('fs').Stats) => string) | 'ls' | 'ep'
   log?: any
   timeout?: number
 }