chore: move core package to top folder.

Signed-off-by: Bo-Yi.Wu <appleboy.tw@gmail.com>

core/scheduler.go

@@ -0,0 +1,24 @@
+package core
+
+import (
+	"context"
+
+	runnerv1 "gitea.com/gitea/proto-go/runner/v1"
+)
+
+type Filter struct {
+	Kind   string
+	Type   string
+	OS     string
+	Arch   string
+	Kernel string
+}
+
+// Scheduler schedules Build stages for execution.
+type Scheduler interface {
+	// Schedule schedules the stage for execution.
+	Schedule(context.Context, *runnerv1.Stage) error
+
+	// Request requests the next stage scheduled for execution.
+	Request(context.Context, Filter) (*runnerv1.Stage, error)
+}