feat: add bun- prefix to cache keys (#160)

* feat: add bun- prefix to cache keys

Extract cache key generation into a shared `getCacheKey` function in
utils.ts that both action.ts and cache-save.ts import.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

* [autofix.ci] apply automated fixes

---------

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>
Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>

src/action.ts

@@ -1,4 +1,3 @@
-import { createHash } from "node:crypto";
 import { homedir } from "node:os";
 import { join } from "node:path";
 import {
@@ -16,7 +15,7 @@ import { getExecOutput } from "@actions/exec";
 import { Registry } from "./registry";
 import { writeBunfig } from "./bunfig";
 import { saveState } from "@actions/core";
-import { addExtension } from "./utils";
+import { addExtension, getCacheKey } from "./utils";
 import { getDownloadUrl } from "./download-url";
 import { cwd } from "node:process";
 
@@ -90,7 +89,7 @@ export default async (options: Input): Promise<Output> => {
 
   if (!revision) {
     if (cacheEnabled) {
-      const cacheKey = createHash("sha1").update(url).digest("base64");
+      const cacheKey = getCacheKey(url);
 
       const cacheRestored = await restoreCache([bunPath], cacheKey);
       if (cacheRestored) {