refactor: ManagedResultArgLoader replaced with ManagedVec iterators #1069

Job	Run time
Contracts (nightly) / Wasm tests	10m 33s
Contracts (nightly) / Rust tests	3m 16s
Contracts (nightly) / Test Coverage	5m 7s
Contracts (nightly) / Clippy linter check	1m 27s
	20m 23s

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