[MerkleDB] Make intermediate node cache two layered #1266

Job	Run time
Unit (macos-12)	6m 27s
Unit (ubuntu-20.04)	4m 31s
Unit (ubuntu-22.04)	4m 35s
Unit (windows-2022)	9m 52s
Protobuf Lint	7s
e2e	7m 4s
Unit (self-hosted, linux, ARM64, focal)	1m 5s
Up-to-date protobuf	21s
Unit (self-hosted, linux, ARM64, jammy)	1m 5s
e2e_existing_network	3m 10s
Fuzz	12m 38s
Lint	3m 3s
Up-to-date mocks	2m 8s
Upgrade	2m 7s
Up-to-date go.mod and go.sum	20s
	58m 33s

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