This pull request aims to improve the error-handling mechanism of the
codebase by providing more descriptive error messages. It involves
changes across multiple files (`cell.rs`, `log.rs`) to add
implementations for the `fmt::Display` trait for `InitError`.

#### Key Changes:

1. **Consistent Formatting**: Replaced `std::fmt` with `fmt` to maintain
consistency in the code.
    - File: `btreemap.rs`
    
2. **Enhanced Error Messages for `InitError` in `cell.rs`**: 
    - Describes errors related to incompatible versions and value sizes.
    
3. **Detailed Error Messages for `InitError` in `log.rs`**: 
- Explains issues with incompatible data and index versions, as well as
invalid indices.

#### Why this is important:

Better error messages enhance the debugging experience and allow
developers to understand the issues quickly, thereby saving time and
effort.

#### Files Changed:
- `src/btreemap.rs`
- `src/cell.rs`
- `src/log.rs`

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

Co-authored-by: Islam El-Ashi <islam.elashi@dfinity.org>

…rait (#142)

### 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:

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

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

```rust
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:
- [x] 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)

Co-authored-by: Roman Kashitsyn <roman.kashitsyn@gmail.com>

Adds a fuzz test that can run indefinitely comparing the results of a
stable BTreeMap to a standard BTreeMap.

I ended up using `proptest` rather than the conventional `cargo fuzz`
for two reasons:

1. `cargo fuzz` requires nightly rust.
2. With proptest, we can have a short version of the fuzz test that runs
as part of CI (which is included in this commit).

#142 introduced some utility methods in the `Bound` struct. We had
copies of these utility methods elsewhere, which are no longer needed
and are removed in this commit.

Adds a short doc on how attributes can be added to a stable structure.

Closes #109

We'd like to support developers changing the bounds of their types from
bounded to unbounded. There were some changes that needed to be made in
this commit in order to make this migration work.

BtreeMap will support deque after this PR #106.
And more methods for BTreeMap for #87

---------

Co-authored-by: Islam El-Ashi <islam.elashi@dfinity.org>