ManagedVec iterator refactor, ManagedVecPayloadIterator #7484

Job	Run time
cargo fmt	25s
Contracts / Test Coverage	10m 24s
Contracts / Interactor tests	20m 28s
Contracts / Clippy linter check	2m 14s
Contracts / Rust tests	5m 25s
Contracts / Wasm tests	20m 16s
	59m 12s

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