Network: stop retry backoff timer on context cancellation

What does this MR do?

This MR replaces time.After with a stoppable timer in the network retry requester.

Using a time.Timer ensures the backoff wait is properly cancelled when the request context is cancelled, preventing timers from lingering across retries.

Why was this MR needed?

time.After allocates a timer that cannot be stopped.
When used inside retry loops, timers may continue running even after the request context is cancelled, leading to unnecessary resource usage.

This change aligns retry behavior in the network package with existing context-aware retry handling in helpers/retry.

What's the best way to test this MR?

go test ./network/...

What are the relevant issue numbers?

N/A