Deny clippy::arithmetic_side_effects for fuel-merkle

[Dentosal]

Closes https://github.com/FuelLabs/fuel-vm/issues/170

Denies the following lints:

• clippy::arithmetic_side_effects
• clippy::cast_sign_loss
• clippy::cast_possible_truncation
• clippy::cast_possible_wrap

Checklist

• [x] Breaking changes are clearly marked as such in the PR description and changelog
• [x] New behavior is reflected in tests

Before requesting review

• [x] I have reviewed the code myself