Memory leak fixes (#4) #101

Job	Run time
prepare	5s
govulncheck	1m 0s
binaries (darwin/amd64)	1m 8s
binaries (darwin/arm64)	1m 6s
binaries (linux/amd64)	2m 22s
binaries (linux/arm/v7)	2m 3s
binaries (linux/arm64)	2m 21s
binaries (linux/s390x)	2m 23s
binaries (linux/ppc64le)	2m 11s
binaries (linux/riscv64)	2m 10s
binaries (windows/amd64)	2m 3s
binaries (windows/arm64)	1m 49s
test / prepare	1m 58s
test / run (containerd, ./client ./cmd/buildctl ./worker/containerd ./solver ./frontend, integration)	7m 39s
test / run (containerd-rootless, ./client ./cmd/buildctl ./worker/containerd ./solver ./frontend, integr...	9m 18s
test / run (containerd-1.6, ./client ./cmd/buildctl ./worker/containerd ./solver ./frontend, integration)	7m 57s
test / run (containerd-snapshotter-stargz, ./client ./cmd/buildctl ./worker/containerd ./solver ./fronte...	8m 45s
test / run (oci, ./client ./cmd/buildctl ./worker/containerd ./solver ./frontend, integration)	5m 38s
test / run (oci-rootless, ./client ./cmd/buildctl ./worker/containerd ./solver ./frontend, integration)	5m 33s
test / run (oci-rootless-slirp4netns-detachnetns, ./client ./cmd/buildctl ./worker/containerd ./solver ....	5m 15s
test / run (oci-snapshotter-stargz, ./client ./cmd/buildctl ./worker/containerd ./solver ./frontend, int...	5m 36s
test / run (./..., 1, integration gateway)	4m 11s
test / run (./client, containerd, nydus, integration)	7m 51s
test / run (./client, oci, nydus, integration)	5m 8s
test / run (./..., nydus, 1, integration)	4m 12s
image	9m 52s
image (rootless)	10m 37s
release	6s
scout	0s
	2h 0m 17s

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