Add PageRank algorithm

[BSZKaneki]

Description

This pull request implements the PageRank algorithm under the graph module.

Algorithm Overview

PageRank is an algorithm used to rank elements in a network based on their structure of incoming links. It computes a probability distribution representing the likelihood that a person randomly clicking on links will arrive at any particular page.

For more details, see the Wikipedia article: https://en.wikipedia.org/wiki/PageRank

Implementation Details

• Genericity: Uses a generic type Node: Hash + Eq + Clone, meaning it can rank nodes of any type (e.g., String, integer types, or custom hashable structures).
• Dangling Nodes: Accurately handles "dangling nodes" (nodes with no outbound edges) by redistributing their rank mass evenly across all nodes in the graph during each iteration.
• Deduplication: Handles duplicate/parallel edges between the same source and destination to prevent artificial weight skewing.
• Convergence: Performs power iteration with an early exit check using an L1 norm difference calculation against a user-defined threshold.
• Testing: Includes 18 tests covering edge cases (such as self-loops, disconnected components, and linear chains) and checking against known analytical results. The entire test suite completes in approximately 0.01s.

Type of change

• New feature (non-breaking change which adds functionality)

Checklist:

• I ran below 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 CONTRIBUTING.md and my code follows its guidelines.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 99.64539% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 95.88%. Comparing base (8ba3163) to head (b30b221).

Files with missing lines	Patch %	Lines
src/graph/page_rank.rs	99.64%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1052      +/-   ##
==========================================
+ Coverage   95.85%   95.88%   +0.02%     
==========================================
  Files         395      396       +1     
  Lines       30160    30442     +282     
==========================================
+ Hits        28910    29189     +279     
- Misses       1250     1253       +3     

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[BSZKaneki]

@siriak Hello could you please take a look at this pull request when you have a moment?

[Copilot]

Pull request overview

Adds a PageRank implementation to the graph module, exposing it publicly and documenting it in the repository’s algorithm directory.

Changes:

• Implemented page_rank in src/graph/page_rank.rs with handling for dangling nodes, duplicate edges, and early convergence.
• Exported the new algorithm from src/graph/mod.rs.
• Added an entry for the new algorithm to DIRECTORY.md.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 6 comments.

File	Description
src/graph/page_rank.rs	New PageRank implementation plus accompanying tests and docs/comments.
src/graph/mod.rs	Registers the new module and re-exports page_rank.
DIRECTORY.md	Adds a directory listing entry linking to the new implementation.

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[siriak]

Please check the comments

[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

[siriak]

Looks good, thanks!