To add missing octal conversions

[NithinU2802]

Description

This__ PR implements the missing octal conversion algorithms to this repository:

• binary_to_octal.rs: Converts binary numbers to octal.
• decimal_to_octal.rs: Converts decimal numbers to octal.
• hexadecimal_to_octal.rs: Converts hexadecimal numbers to octal.
• octal_to_hexadecimal.rs: Converts octal numbers to hexadecimal.

Please let me know if any changes required I'm happy to update accordingly🚀

Closes #929

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 95.35%. Comparing base (7763020) to head (03cc250).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #931      +/-   ##
==========================================
+ Coverage   95.32%   95.35%   +0.02%     
==========================================
  Files         319      323       +4     
  Lines       20895    21003     +108     
==========================================
+ Hits        19919    20027     +108     
  Misses        976      976              

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