test(e2e): speed up and cover exec and Kubernetes modes (#1363)

Follow-up to https://gitea.com/gitea/runner/pulls/1362, whose crash e2e missed because it only drove the daemon on Docker.

- `dispatch`, `failure_paths` and `reusable_workflow` run through the daemon and `exec`, each on Docker and one shared k3s cluster.
- Fixed sleeps become gates the test releases, the job timeout uses a 15s runner deadline, k3s boots alongside Gitea, Gitea's data is on tmpfs.
- Outside a container, `make test-e2e` runs `go test` in a Linux container on its own network like CI, so local runs take the same paths.

Local wall time:

| | Before | After |
|---|---|---|
| Suite | 84s | 27–35s |
| `job_timeout` | 64s | 17s |
| `reconnect` | 22s | 4.5s |
| `capacity/serial` | 20s | 2s |
| `cli_shutdown_drains` | 14s | 2.3s |
| `kubernetes` | 31s | 21–23s |

_Written by Claude (Opus 5.5)._

---------

Co-authored-by: bircni <[email protected]>
Reviewed-on: https://gitea.com/gitea/runner/pulls/1363
Reviewed-by: bircni <[email protected]>
Co-authored-by: silverwind <[email protected]>

e2e/reusable_test.go

@@ -8,15 +8,12 @@ package e2e
 import "testing"
 
 // testReusableWorkflow runs a local workflow_call workflow and consumes its output.
-func testReusableWorkflow(t *testing.T) {
-	t.Parallel()
-	api, repo := newScenario(t)
-	pushWorkflow(t, api, repo, "reusable_callee.yml")
-	pushWorkflow(t, api, repo, "reusable_caller.yml")
-
-	wfRun := waitForRun(t, api, repo)
-	requireSuccess(t, api, repo, wfRun.ID)
-	if logs := runLogs(t, api, repo, wfRun.ID); commandRow(logs, "e2e-reusable-ran") == "" {
-		t.Errorf("the called workflow did not run:\n%s", logs)
+func testReusableWorkflow(t *testing.T, m mode) {
+	result := runWorkflow(t, m, workflowSpec{
+		files:    []string{"reusable_callee.yml", "reusable_caller.yml"},
+		execArgs: []string{"--no-skip-checkout"},
+	})
+	if result.conclusion != "success" || !result.hasLine("e2e-reusable-ran") {
+		t.Errorf("run concluded %q, want success with the called workflow's marker", result.conclusion)
 	}
 }