test : add unit tests for upstash-rest.ts getUpstashConfig #3031

Summary of What Needs to be Done: Add unit tests for src/lib/upstash-rest.ts, specifically the getUpstashConfig() function. This is the only pure function in the module — all other functions make network calls to the Upstash API and require mocking fetch.

Changes that Need to be Made:

• Create test/upstash-rest.test.ts with Vitest
• Test getUpstashConfig: when UPSTASH_REDIS_REST_URL and UPSTASH_REDIS_REST_TOKEN are both set in env, verify it returns { url, token }; when either is missing, verify it returns null; when either is empty string, verify it returns null

Impact that it would Provide: getUpstashConfig is the configuration gate for the entire Upstash integration. Tests prevent regression when env var names change or when the null-guard logic is accidentally modified. The test is fast and requires no network mocking.

Hello @Priyanshu-byte-coder, please assign this issue to me (@tmdeveloper007) so I can open a focused PR.