GetIDs API return the DA blocktime

[gupadhyaya]

For based sequencing (e.g., using celestia for sequencing), we need the DA blocktime time.Time to be made available as part of GetIDs API. GetIDs(ctx context.Context, height uint64, namespace Namespace) ([]ID, error) such that, sequencer can return this as part of GetNextBatch (https://github.com/rollkit/go-sequencing/blob/main/sequencing.go#L26).

Updated GetIDs API:
GetIDs(ctx context.Context, height uint64, namespace Namespace) ([]ID, time.Time, error)