Version check HTTP request has no timeout or cancellation

Expected Behavior

The server version check should have a bounded deadline. Stopping the
VersionChecker should cancel an in-flight version-info request and allow the
background goroutine to exit.

Actual Behavior

The server version check can remain blocked indefinitely when the version-info
endpoint accepts the request but never sends a response.

common/versioninfo.Caller.Call creates an http.Client without a timeout and
uses http.NewRequest without a context. service/frontend.VersionChecker
runs the check in a background goroutine and currently uses context.TODO().

Because VersionChecker.Stop() only closes the shutdown channel, an in-flight
version check cannot be cancelled and the goroutine does not exit until the HTTP
request returns.

This does not block frontend startup, since the check runs in a goroutine, but
it can leave a background goroutine and HTTP connection stuck indefinitely.

Steps to Reproduce the Problem

1. Check out the Temporal server main branch and create an httptest.Server
   whose handler accepts the request and then waits indefinitely.
2. Configure a versioninfo.Caller to use the test server and call Caller.Call
   with a valid VersionCheckRequest.
3. Wait for a bounded period, such as 300 ms, for Caller.Call to return.
4. Observe that the call is still blocked. The same behavior leaves an
   in-flight request inside VersionChecker uncancellable by Stop().

I reproduced this locally with an httptest.Server; Caller.Call was still
blocked after 300 ms.

Specifications

• Version: main as of 2026-09-05; go.mod requires Go 1.26.4
• Platform: Windows host with PowerShell; the behavior should be platform-independent

Possible Direction

Would it make sense to propagate a context to Caller.Call, apply a bounded
timeout to the version-info request, and cancel the checker context from
VersionChecker.Stop()?

A regression test using an httptest.Server that never responds should verify
that the request returns with a timeout or cancellation error.

No persistence, protocol, or protobuf changes should be required.

Start with common/versioninfo.Caller.Call and service/frontend.VersionChecker, then trace how the current context and shutdown channel are used. Use an httptest.Server that accepts a request without responding to verify the request gets a bounded timeout or cancellation and VersionChecker.Stop() lets the background goroutine exit.