Refactor Caesar Algorithm Implementation

[StPfeffer]

Description

Refactored the Caesar algorithm to handle larger inputs and rotations while preserving the existing code structure. Included additional tests for improved coverage.

Type of change

• [x] Bug fix (non-breaking change which fixes an issue)

Checklist:

• [x] I ran bellow commands using the latest version of rust nightly.
• [x] I ran cargo clippy --all -- -D warnings just before my last commit and fixed any issue that was found.
• [x] I ran cargo fmt just before my last commit.
• [x] I ran cargo test just before my last commit and all tests passed.
• [x] I added my algorithm to the corresponding mod.rs file within its own folder, and in any parent folder(s).
• [x] I added my algorithm to DIRECTORY.md with the correct link.
• [x] I checked COUNTRIBUTING.md and my code follows its guidelines.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 94.86%. Comparing base (0aa3f8d) to head (327bafb). Report is 1 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #720 +/- ## ======================================= Coverage 94.85% 94.86% ======================================= Files 302 302 Lines 22575 22590 +15 ======================================= + Hits 21414 21429 +15 Misses 1161 1161 ```

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.

[StPfeffer]

What do you think about defining the 26 as some constant. It could be computed as a difference between a and z (plus 1, I think).

That's a good idea. I defined it as:

const ALPHABET_LENGTH: u8 = b'z' - b'a' + 1;