Feature/exponential backoff

[dgomesbr]

Feature/exponential backoff added to both Sonarr and Radarr clients with sensible defaults.

[nullable-eth]

Hey @dgomesbr, thanks for these contributions! The batch processing and exponential backoff features look solid and address real issues for users with large libraries.

I found a couple of issues:

🔴 Bug: Missing time import in internal/config/config_test.go

The TestBackwardCompatibility function references time.Hour on line 185, but the time package isn't imported. Quick fix:

import (
	"os"
	"testing"
	"time"  // <- add this
)

⚠️ Potential Issue: Request body not re-readable on retry

In internal/utils/retry.go, the retry logic clones the request but doesn't handle request body re-reading:

reqClone := req.Clone(ctx)

If any request has a body (POST/PUT), the body stream will be consumed on the first attempt, and subsequent retries will send an empty body. While this may not be an issue currently since the Radarr/Sonarr clients only make GET requests, it could cause subtle bugs if POST/PUT requests are added later.

A safer approach would be to use GetBody if available, or buffer the body for retries:

if req.GetBody != nil {
    body, err := req.GetBody()
    if err == nil {
        reqClone.Body = body
    }
}

Not a blocker for this PR since the current usage is GET-only, but worth noting for future-proofing.

---

Also, since this PR contains all the changes from PR #27 plus the exponential backoff feature, I'll close #27 as superseded by this one.

Once the import fix is in, this should be good to merge! 🚀