Added C# and F# examples

[a-gubskiy]

This pull request introduces complete implementations of single and double linked lists in both C# and F#, adds supporting project and entry point files, and corrects single linked list node direction in JavaScript examples. The changes provide working code samples for each language, demonstrating list construction and traversal.

Linked List Implementations

• Added full implementations of single and double linked lists in C# (SingleLinked.cs, DoubleLinked.cs), including node classes, list operations, and example usage. [1] [2]
• Added full implementations of single and double linked lists in F# (SingleLinked.fs, DoubleLinked.fs), including node types, list operations, and example usage. [1] [2]

Project and Entry Point Setup

• Added C# and F# project files (HowProgrammingWorks.CS.csproj, HowProgrammingWorks.FS.fsproj) and entry point files (Program.cs, Program.fs) to enable compilation and execution of the examples. [1] [2] [3] [4]

JavaScript Example Corrections

• Fixed the direction of node links in JavaScript single linked list examples (1-single-proto.js, 2-single-factory.js), changing from prev to next and updating usage accordingly. [1] [2]

[a-gubskiy]

@tshemsedinov any news or thoughts about this PR? :)

[a-gubskiy]

@tshemsedinov let's merge it?