Enable storing of a Vec with the StorageVec type

[bitzoic]

Description

Currently, StorageVec and Vec do not have any relation with one another. This PR takes advantage of the recent optimization and refactoring done to the Storage API read() and write() functions in #4795 and enables the storing of a Vec using the StorageVec type.

To do this, the StorageVec now stores things sequentially rather than a different key for every element. Due to the optimizations done to the Storage API, this has become feasible as we can now load a single element of the sequential StorageVec.

The storing of elements sequentially mimics the existing Vec, allowing us to store it as a raw_slice with a single read/write to storage as opposed to looping over the Vec and having n read/writes.

It should be noted that due to #409, the storing of a Vec is written in the StorageVec file. This is the resulting syntax:

let my_vec = Vec::new();
storage.storage_vec.store_vec(my_vec); // Store the Vec
let other_vec = storage.storage_vec.load_vec(); // Read the Vec

When this issue is resolved, this should be changed to a From implementation changing the syntax to:

let my_vec = Vec::new();
storage.storage_vec = my_vec.into(); // Store the Vec
let other_vec = Vec::from(storage.storage_vec); // Read the Vec

Closes #2439

Checklist

• I have linked to any relevant issues.
• I have commented my code, particularly in hard-to-understand areas.
• I have updated the documentation where relevant (API docs, the reference, and the Sway book).
• I have added tests that prove my fix is effective or that my feature works.
• I have added (or requested a maintainer to add) the necessary Breaking* or New Feature labels where relevant.
• I have done my best to ensure that my PR adheres to the Fuel Labs Code Review Standards.
• I have requested a review from the relevant team or maintainers.

[K1-R1]

lgtm