fix: paginate ListNotCompletedDeployments in legacy piped

[Goyamjain06]

What this PR does

Updates the legacy piped deployment store to follow the pagination cursor returned by ListNotCompletedDeployments.

Previously, sync() fetched only the first page and ignored the returned cursor. It now continues fetching until the cursor is empty, ensuring all pending/planned/running deployments are included.

Changes

• Update pkg/app/piped/apistore/deploymentstore/store.go to paginate ListNotCompletedDeployments using resp.Cursor.
• Add store_test.go with coverage for:
  • empty responses
  • deployment status classification
  • multi-page pagination
  • 3+ page pagination
  • ROLLING_BACK classification
  • errors during pagination
• No proto, server, controller, or unrelated changes.

Tests

• go test ./pkg/app/piped/apistore/deploymentstore/... — pass
• go vet ./pkg/app/piped/apistore/deploymentstore/... — pass
• make check — Go build and web build pass. The golangci-lint step is blocked by the pinned lint image using Go 1.25.0 while the repository requires Go 1.26.2.

Fixes #1937

[github-actions]

👋 Hi @Goyamjain06, welcome to PipeCD and thanks for opening your first pull request!

We’re really happy to have you here

Before your PR gets merged, please check a few important things below.

---

Helpful resources

• Contributing guide: https://github.com/pipe-cd/pipecd/blob/master/CONTRIBUTING.md
• Development setup: https://github.com/pipe-cd/pipecd/blob/master/CONTRIBUTING.md#development

---

DCO Sign-off

All commits must include a Signed-off-by line to comply with the Developer Certificate of Origin (DCO).

In case you forget to sign-off your commit(s), follow these steps:

For the last commit:

git commit --amend --signoff
git push --force-with-lease

For multiple commits:

git rebase --signoff origin/master
git push --force-with-lease

---

Run checks locally

Before pushing updates, please run:

make check

This runs the same checks as CI and helps catch issues early.

---

💬 Need help?

If anything is unclear, feel free to ask in this PR or join us on the CNCF Slack in the #pipecd channel.
You can get your Slack invite from: https://communityinviter.com/apps/cloud-native/cncf

Thanks for contributing to PipeCD! ❤️