Migrate to ESM and upgrade dependencies (#763)

* Migrate to ESM and upgrade dependencies

* Remove unused tsconfig.eslint.json

* bump version to 7.0.0 in package.json and package-lock.json

* Add ESM migration note to README for V7

* Remove unnecessary devDependencies: ts-node, @types/jest

* npm audit fix

* Update README with ESM migration details

Clarified migration details to ESM for action compatibility.

* Downgrade @types/node to ^24, clean up tsconfig and README.

src/go-version-fetch.ts

@@ -0,0 +1,13 @@
+import * as httpm from '@actions/http-client';
+import type {IGoVersion} from './installer.js';
+
+export async function getVersionsDist(
+  dlUrl: string
+): Promise<IGoVersion[] | null> {
+  // this returns versions descending so latest is first
+  const http: httpm.HttpClient = new httpm.HttpClient('setup-go', [], {
+    allowRedirects: true,
+    maxRedirects: 3
+  });
+  return (await http.getJson<IGoVersion[]>(dlUrl)).result;
+}