fix: stop leaking per-job docker networks (#1124)

Leaked per-job networks each hold a subnet of the daemon's address pool and nothing reclaimed them, so a host eventually fails every job with `all predefined address pools have been fully subnetted`. This is what CI hit in https://gitea.com/gitea/runner/actions/runs/742177.

- teardown no longer loses a container, and its network with it: a failed `ContainerRemove` was reported as success, a container whose id was never learned was skipped, and the daemon's own `AutoRemove` teardown was raced
- the idle cleanup reclaims what teardown cannot: networks carry `com.gitea.runner.uuid`, so a runner only touches its own, and a cutoff keeps a job starting during the pass out of scope
- pull failures reported mid-stream were discarded, surfacing later as a confusing `No such image`; they now propagate, and fall back to a local copy instead of failing the job
- `NetworkCreate` retries pool exhaustion briefly, then says which knobs to turn
- digest-pinned images are not re-pulled, and removal kills first so it never waits out Podman's stop timeout (measured 10.1s → 0.09s per container)

---------

Co-authored-by: bircni <bircni@icloud.com>
Reviewed-on: https://gitea.com/gitea/runner/pulls/1124
Reviewed-by: bircni <bircni@icloud.com>

act/container/docker_stub.go

@@ -9,6 +9,7 @@ package container
 import (
 	"context"
 	"runtime"
+	"time"
 
 	"gitea.com/gitea/runner/act/common"
 
@@ -72,3 +73,7 @@ func NewDockerNetworkRemoveExecutor(name string) common.Executor {
 		return nil
 	}
 }
+
+func RemoveOrphanNetworks(ctx context.Context, runnerUUID string, createdBefore time.Time) error {
+	return nil
+}