feat: add task assignment problem using bitmasking and DP

[AliAlimohammadi]

Description

Adds implementation of the Task Assignment Problem using bitmasking and dynamic programming.

Problem Statement

Given:

• N tasks to be performed
• M people who can perform tasks
• Each person can perform only certain tasks
• Each person can perform at most one task
• Each task can be performed by at most one person

Find the total number of valid task assignments where all people are assigned tasks.

Algorithm

• Uses bitmasking to represent which people have been assigned tasks
• Uses dynamic programming to cache subproblem results
• Recursively tries assigning each task to capable people

Complexity

• Time: O(2^M * N) where M is number of people, N is number of tasks
• Space: O(2^M * N) for the DP table

Example

let task_performed = vec![vec![1, 3, 4], vec![1, 2, 5], vec![3, 4]];
let total_tasks = 5;
let ways = count_task_assignments(task_performed, total_tasks);
// Returns: 10 valid assignments

Checklist

• Code follows Rust style guidelines (rustfmt)
• No clippy warnings
• All tests pass
• Added comprehensive test cases
• Documentation is complete
• Updated DIRECTORY.md
• Updated mod.rs

[codecov-commenter]

Codecov Report

❌ Patch coverage is 98.07692% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 95.45%. Comparing base (1ce9f3a) to head (98ca061).

Files with missing lines	Patch %	Lines
src/dynamic_programming/task_assignment.rs	98.07%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #958   +/-   ##
=======================================
  Coverage   95.44%   95.45%           
=======================================
  Files         333      334    +1     
  Lines       21524    21576   +52     
=======================================
+ Hits        20544    20595   +51     
- Misses        980      981    +1     

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[AliAlimohammadi]

@siriak, This is ready to merge.

[siriak]

Looks good, thanks!