Align codec interface to exclusively use packers #7939

Job	Run time
Protobuf Lint	11s
Up-to-date mocks	2m 4s
Up-to-date protobuf	27s
e2e_existing_network	4m 5s
e2e_post_etna	11m 31s
e2e_pre_etna	11m 32s
Fuzz	13m 26s
Up-to-date go.mod and go.sum	10s
Lint	3m 21s
Build Antithesis avalanchego images	8m 33s
Build Antithesis xsvm images	11m 50s
Image build	10m 39s
Upgrade	3m 12s
Unit (macos-12)	8m 46s
Unit (ubuntu-20.04)	4m 26s
Unit (ubuntu-22.04)	6m 46s
Unit (windows-2022)	11m 34s
Unit (custom-arm64-focal)	8m 48s
Unit (custom-arm64-jammy)	12m 10s
	2h 13m 31s

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