Refactor Pangram Implementation

[sozelfist]

Checklist:

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

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.33%. Comparing base (155c767) to head (2ce0f0d).

Additional details and impacted files

@@ Coverage Diff @@ ## master #795 +/- ## ========================================== - Coverage 95.33% 95.33% -0.01%  ========================================== Files 310 310 Lines 22518 22493 -25 ========================================== - Hits 21468 21443 -25  Misses 1050 1050 

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[sozelfist]

Can you have a look, @vil02?

[sozelfist]

Can you review this PR, @vil02, it stands here for a week.

[vil02]

There was still some margin for improvement.