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/runner_harness.go

@@ -33,6 +33,7 @@ type runnerOptions struct {
 	host       bool   // register a host-mode label instead of a docker one
 	name       string // suffix that keeps runner names unique when a test starts several
 	address    string // Gitea address the runner talks to, default the fixture
+	timeout    time.Duration
 }
 
 func startRunner(t *testing.T, repo, labelName string, options runnerOptions) *poll.Poller {
@@ -60,9 +61,8 @@ func startRunner(t *testing.T, repo, labelName string, options runnerOptions) *p
 	cfg.Runner.StateReportInterval = 500 * time.Millisecond // so cancel reaches the job quickly
 	cfg.Runner.LogReportInterval = 500 * time.Millisecond
 	cfg.Runner.Capacity = max(options.capacity, 1)
-	if fixture.network != "" {
-		cfg.Container.Network = fixture.network
-	}
+	cfg.Runner.Timeout = cmp.Or(options.timeout, cfg.Runner.Timeout)
+	cfg.Container.Network = fixture.network
 
 	scheme := labels.SchemeDocker
 	if options.kubernetes != nil {