Add Binary Coded Decimal algorithm to bit manipulation

[AliAlimohammadi]

Description

Adds the Binary Coded Decimal (BCD) algorithm to the bit manipulation module.

This algorithm converts a decimal integer to Binary Coded Decimal format, where each decimal digit is represented by its 4-bit binary equivalent.

Implementation Details

• Converts each decimal digit (0-9) to a 4-bit binary representation
• Uses fold with write! macro for efficient string building
• Handles negative numbers by treating them as 0 (matching Python implementation)
• Returns result with "0b" prefix for consistency
• Time Complexity: O(n) where n is the number of digits
• Space Complexity: O(n) for the output string

Examples

binary_coded_decimal(12)   // Returns "0b00010010" (1=0001, 2=0010)
binary_coded_decimal(987)  // Returns "0b100110000111" (9=1001, 8=1000, 7=0111)
binary_coded_decimal(-5)   // Returns "0b0000" (negative → 0)

Testing

• Added comprehensive unit tests covering:
  • Zero and single digits (0-9)
  • Two-digit numbers
  • Three-digit numbers
  • Large numbers (4+ digits)
  • Negative numbers
  • Specific digit encoding verification
• All tests pass with cargo test
• Doctests pass with correct import paths
• Code formatted with cargo fmt
• No clippy warnings (uses fold and write! for efficiency)

Checklist

• I have tested the code
• I have run cargo fmt
• I have run cargo clippy
• I have added documentation
• I have added tests

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.63%. Comparing base (e877687) to head (b1ba689).

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #966   +/-   ##
=======================================
  Coverage   95.62%   95.63%           
=======================================
  Files         339      340    +1     
  Lines       22078    22127   +49     
=======================================
+ Hits        21113    21161   +48     
- Misses        965      966    +1     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[AliAlimohammadi]

@siriak, this is ready to be merged.