Improve normalize in karatsuba_multiplication implementation

[dxdw233]

Pull Request Template

Description

Refactor normalize in karatsuba_multiplication.rs to improve performance and readability.

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

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.

Please make sure that if there is a test that takes too long to run ( > 300ms), you #[ignore] that or
try to optimize your code or make the test easier to run. We have this rule because we have hundreds of
tests to run; If each one of them took 300ms, we would have to wait for a long time.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.51%. Comparing base (1dbf1a0) to head (8d6956d).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #881      +/-   ##
==========================================
- Coverage   95.51%   95.51%   -0.01%     
==========================================
  Files         317      317              
  Lines       22955    22954       -1     
==========================================
- Hits        21925    21924       -1     
  Misses       1030     1030              

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