support for async call to repo sync by adding new method

[3choBoomer]

Summary

Adds a new RepoListSyncAsync() method to the Client interface and its implementation. It posts to the same endpoint as RepoListSync but with async=true appended to the URL, causing the server to trigger the sync and return immediately.

This is one of two proposed approaches to resolve #74, which has been open since 2024. See #XX for an alternative implementation that extends RepoListSync with a functional options pattern instead.

Changes

• Adds RepoListSyncAsync() ([]*Repo, error) to the Client interface
• Adds the corresponding (c *client) RepoListSyncAsync() implementation in client.go
• RepoListSync is untouched

Usage

// Existing — blocking sync, unchanged
repos, err := client.RepoListSync()

// New — non-blocking async sync
repos, err := client.RepoListSyncAsync()

Notes

This approach keeps each method's intent explicit and self-documenting — the function name alone communicates the async behaviour without requiring callers to know about option constructors.

Alternatives

See #75 for an alternative that extends RepoListSync with a functional options pattern instead. That approach keeps the Client interface surface smaller and is more extensible if additional query parameters are needed in the future, at the cost of a slightly less obvious call site.

[CLAassistant]

All committers have signed the CLA.

[Ompragash]

thanks for the PR! The approach of adding a dedicated method is clean and non-breaking. nice work.

[ebtasam-faridy]

Hi @3choBoomer 3choBoomer,
Would it be possible to sync briefly before we move forward with this PR? I have a couple of suggestions:

1. The async server path returns 204 No Content (empty body), but the current client flow still tries to JSON-decode the response body. That can surface as an EOF error.
2. It would help to add focused tests for this behaviour:
   a client-side test for async sync behaviour
   a test that explicitly validates handling of empty/204 responses from drone/drone

[3choBoomer]

@Ompragash @ebtasam-faridy I am currently traveling with family and I will circle back with you guys when I return to work on Thursday.