Solution to manage routing answers

[castelao]

New Solution to hold routing solution. More methods will be implemented, but for now the goal is to hide its composition to make it easier the larger refactoring under way.

[Copilot]

Pull Request Overview

This PR introduces a structured Solution type to encapsulate routing results, replacing the previous tuple-based approach for better type safety and code clarity.

• Adds a new Solution<I, C> struct to represent routing solutions with route and cost data
• Refactors routing methods to return Solution instances instead of (Vec<ArrayIndex>, f32) tuples
• Updates all test cases to use the new Solution API methods

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 7 comments.

File	Description
crates/revrt/src/solution.rs	Defines the new Solution struct with generic route and cost types
crates/revrt/src/routing/mod.rs	Updates routing methods to return Solution instances and removes commented code
crates/revrt/src/lib.rs	Integrates Solution usage and updates all test cases to use new API

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