chore(userspace/libsinsp): keep a reference on m_sinsp_stats_v2 where needed #1074

Job	Run time
build-test-e2e-amd64 😇 (bundled_deps)	14m 46s
build-test-e2e-arm64 😇 (bundled_deps)	13m 31s
test-e2e-amd64-kmod 😇 (bundled_deps)	4m 47s
test-e2e-amd64-bpf 😇 (bundled_deps)	4m 47s
test-e2e-amd64-modern-bpf 😇 (bundled_deps)	4m 33s
test-e2e-arm64-kmod 😇 (bundled_deps)	6m 12s
test-e2e-arm64-bpf 😇 (bundled_deps)	5m 54s
test-e2e-arm64-modern-bpf 😇 (bundled_deps)	5m 56s
	1h 0m 26s

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