feat: add solutions to lc problem: No.3286

[yanglbme]

Summary

• Add C# and Rust solutions for 3286. Find a Safe Walk Through a Grid
• Update Chinese and English READMEs with the new solution code blocks

Test plan

• Verify C# and Rust solutions compile
• Confirm README code blocks match Solution.cs and Solution.rs
• Run against LeetCode test cases for No.3286

[Copilot]

Pull request overview

This PR adds missing language implementations for LeetCode #3286 (Find a Safe Walk Through a Grid) to the repository’s standard per-problem solution folder, and updates the per-problem READMEs to include the new language code blocks alongside existing solutions.

Changes:

• Add a Rust solution (Solution.rs) implementing the same shortest-path-with-relaxation approach used by existing language solutions for this problem.
• Add a C# solution (Solution.cs) mirroring the repository’s established pattern for grid shortest-path solutions.
• Update both README.md and README_EN.md to include the Rust and C# solution code blocks.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
solution/3200-3299/3286.Find a Safe Walk Through a Grid/Solution.rs	Adds Rust implementation for problem 3286.
solution/3200-3299/3286.Find a Safe Walk Through a Grid/Solution.cs	Adds C# implementation for problem 3286.
solution/3200-3299/3286.Find a Safe Walk Through a Grid/README.md	Adds Rust and C# code blocks to the Chinese README tabs.
solution/3200-3299/3286.Find a Safe Walk Through a Grid/README_EN.md	Adds Rust and C# code blocks to the English README tabs.

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