feat: Add constructor

[Sirivasv]

Fixes #24

[Copilot]

Pull Request Overview

This PR adds a constructor to the BMSSP (Bidirectional Multi-Source Shortest Path) class, replacing the previous simple message functions with a proper graph data structure initialization.

• Introduces a BMSSP class with a constructor that accepts and deep copies input graph data
• Updates all imports and examples to use the new BMSSP class instead of message functions
• Adds comprehensive test documentation and sets up test infrastructure with real-world road network data

Reviewed Changes

Copilot reviewed 6 out of 7 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/bmssp.mjs	Replaces message functions with BMSSP class and constructor
index.mjs	Updates exports to expose BMSSP class
test/main.test.mjs	Replaces message tests with constructor tests using California road network data
test/README.md	Adds comprehensive test documentation and dataset information
examples/main.mjs	Updates example to demonstrate BMSSP constructor usage
README.md	Updates usage example to show BMSSP class instantiation

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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