Refactor Pangram Implementation

[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.

[codecov-commenter]

Codecov Report

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

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.