Rename reentrancy guard

[adlerjohn]

Either rename or better document the reentrancy guard. The guard only protects against control flow hijacking on a single contract, not multiple trusted contracts working together. While the latter case may be less common on Fuel due to a larger contract size limit, it will still happen.

See more: https://inspexco.medium.com/cross-contract-reentrancy-attack-402d27a02a15

The guard should also be documented to not be needed if CEI is followed, which is enforced by the compiler.

[mohammadfawaz]

cc @jtriley-eth - I transferred this issue from the Sway repo.