feat: Enhance Bound Enum with Utility Methods and Refactor Storable Trait

[b3hr4d]

Description:

This PR introduces utility methods to the Bound enum, enhancing its functionality and usability. These methods are used to refactor the Storable trait, making it cleaner and more maintainable.

Use-Case:

I am developing a library aimed at simplifying the use of stable memory structures. For example, consider a TaskTimerEntry struct defined as:

pub struct TaskTimerEntry<T> {
    pub time: NanoTimeStamp,
    pub task: T,
}

To make this struct bounded, I can now easily specify:

const BOUND: Bound = Bound::Bounded {
    is_fixed_size: false,
    max_size: 8 + T::BOUND.max_size(),
};

Key Changes:

Introduced max_size and is_fixed_size methods to Bound enum.

Impact on Storable Trait:

The utility methods have been integrated into the Storable trait, enhancing its readability and maintainability without altering its core functionality.

Types of Changes:

• New feature (non-breaking change which adds functionality)
• Bugfix (non-breaking change which fixes an issue)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation Update (if none of the other choices apply)

[ielashi]

LGTM, thanks! It'd be great if you could update the description to fit the new changes.