feat: add method DoubleFactorial

[khanhkhanhlele]

This PR adds method DoubleFactorial.
Contribution by Gittensor, learn more at https://gittensor.io/

[Copilot]

Pull Request Overview

This PR adds a DoubleFactorial implementation that calculates the double factorial (n!!) of non-negative integers, which is the product of all integers from 1 up to n that have the same parity as n.

• Adds DoubleFactorial.Calculate() method that handles both odd and even cases using BigInteger
• Includes comprehensive test coverage for base cases, odd/even numbers, large numbers, and negative input validation

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 5 comments.

File	Description
Algorithms/Numeric/DoubleFactorial.cs	Implements the double factorial calculation with BigInteger support for large numbers
Algorithms.Tests/Numeric/DoubleFactorialTests.cs	Adds unit tests for valid inputs and negative number edge cases

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.90%. Comparing base (6c3203b) to head (5e57006).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #567      +/-   ##
==========================================
- Coverage   96.90%   96.90%   -0.01%     
==========================================
  Files         294      295       +1     
  Lines       12188    12204      +16     
  Branches     1767     1770       +3     
==========================================
+ Hits        11811    11826      +15     
  Misses        239      239              
- Partials      138      139       +1     

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[siriak]

Please check the comments

[Copilot]

Pull Request Overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

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[siriak]

Looks good, thanks!