Migrate pallet-mmr to umbrella crate #9521

Job	Run time
preflight / preflight	42s
preflight / ci-versions	53s
cargo-check-benches (master)	20m 57s
cargo-check-benches (current)	24m 12s
cargo-check-all-crate-macos	11m 28s
test-frame-ui	27m 2s
cargo-check-each-crate (1)	20m 37s
cargo-check-each-crate (2)	19m 23s
test-full-crypto-feature	2m 28s
test-node-metrics	10m 25s
cargo-check-each-crate (3)	8m 0s
cargo-check-each-crate (4)	18m 33s
cargo-check-each-crate (5)	27m 10s
cargo-check-each-crate (6)	13m 14s
cargo-check-each-crate (7)	27m 27s
test-frame-examples-compile-to-wasm	2m 55s
test-deterministic-wasm	7m 35s
check-tracing	2m 14s
check-metadata-hash	6m 43s
node-bench-regression-guard	16s
All test misc tests passed	1s
	4h 12m 15s

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