feat: add integration test suite for CLI lifecycle

[TimPietruskyRunPod]

Summary

runpodctl currently lacks integration tests that exercise the full CLI lifecycle. An integration test suite would help catch regressions and validate end-to-end behavior.

Desired behavior

• A test suite that covers the full lifecycle of key resources:
  • Pods: create → list → get → update → stop → start → delete
  • Serverless: create → list → get → update → delete
  • File transfer: send/receive via croc
• A GitHub Actions workflow that runs the suite with gated API key access
• Tests should gracefully handle missing API keys (e.g. on external fork PRs)
• Resource cleanup must be scoped — only clean up resources created by the test run (e.g. using a name prefix like ci-test-), never delete all account resources
• Template IDs and other config should be parameterized (env vars), not hardcoded
• Use trap for cleanup to ensure resources are removed even if tests fail

Related PRs

• feat: portable, root-free installer refactor (dependency-free) #240 and feat: unified integration matrix with gated CI signaling #241 proposed this feature but need rework — see comments on those PRs for details

Notes

• Integration tests create real billable resources, so they should use CPU-only compute and minimal templates
• The CI workflow should only trigger on main and PRs to main (no hardcoded feature branch names)
• Consider using Go-based e2e tests (the project already has a go test -tags e2e convention) rather than shell scripts