feat: add Minimum Coin Change greedy algorithm

[AliAlimohammadi]

Description

Overview

Implements the minimum coin change problem using a greedy algorithm.

What's Added

• minimum_coin_change.rs in src/greedy/
• Greedy algorithm to find minimum coins needed for making change
• Works optimally for canonical coin systems (USD, EUR, INR, etc.)

Algorithm Complexity

• Time: $O(n)$ where n = number of denominations
• Space: $O(m)$ where m = number of coins in result

Implementation Details

• Always selects the largest denomination possible at each step
• Handles edge cases: zero value, negative values, empty denominations
• Sorts denominations automatically for optimal selection
• Returns empty vector for invalid inputs

Tests Included

✅ Indian currency standard (987 rupees)
✅ Large amounts (18,745)
✅ Zero and negative values
✅ Non-standard denominations
✅ Single denomination
✅ Exact denomination match
✅ Empty denominations
✅ Unsorted input
✅ USD currency (cents)

Documentation

• Module-level documentation with algorithm explanation
• Function-level doc comments with examples
• Self-contained doctests (no external imports needed)
• Inline code comments for clarity
• Examples demonstrate various use cases
• All doctests compile and pass

Files Changed

• src/greedy/minimum_coin_change.rs (new file)
• src/greedy/mod.rs (added module declaration)

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Checklist

• Follows Rust naming conventions
• Comprehensive documentation with examples
• All public functions have doc comments
• Unit tests included and passing
• Updated mod.rs
• No compiler warnings
• Clippy passes cleanly
• Formatted with cargo fmt

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.94%. Comparing base (f92b944) to head (f1431da).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #992      +/-   ##
==========================================
+ Coverage   95.93%   95.94%   +0.01%     
==========================================
  Files         361      362       +1     
  Lines       24613    24685      +72     
==========================================
+ Hits        23612    23685      +73     
+ Misses       1001     1000       -1     

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[AliAlimohammadi]

@siriak, this is ready to be merged.