Refactor Anagram

[sozelfist]

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.

[sozelfist]

Can you have a look, @vil02?

[codecov-commenter]

Codecov Report

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

Project coverage is 95.40%. Comparing base (858443e) to head (bd326fc).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #825 +/- ## ======================================= Coverage 95.40% 95.40% ======================================= Files 313 313 Lines 22699 22708 +9 ======================================= + Hits 21655 21664 +9 Misses 1044 1044 ```

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