Refactor directory walk into an iterator pattern

[svasista-ms]

Refactor opportunity:
The logic of reading directories, identifying cargo projects by Cargo.toml, figuring out if there is atleast one valid rust project or action failure etc could be abstracted into a custom Iterator (E.g: CargoProjectIterator) which we could be used in clean and build actions. This improves consistency across build and clean actions right now and any actions we may add later.

Originally posted by Krishna Kumar Thokala (@krishnakumar4a4) in #638