Simplify common.Engine API #8299

Job	Run time
Up-to-date protobuf	22s
e2e_existing_network	51s
Up-to-date mocks	49s
Protobuf Lint	6s
e2e_post_etna	49s
e2e_pre_etna	48s
Fuzz	49s
Up-to-date go.mod and go.sum	13s
Lint	46s
Build Antithesis avalanchego images	48s
Build Antithesis xsvm images	48s
Image build	49s
Unit (macos-12)	48s
Upgrade	49s
Unit (ubuntu-20.04)	47s
Unit (ubuntu-22.04)	46s
Unit (ubuntu-24.04)	45s
Unit (windows-2022)	42s
Unit (custom-arm64-jammy)	42s
Unit (custom-arm64-noble)	42s
	13m 59s

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