♻️ Make playground parse README.md bulk-selectable and copyable using Rust for better performance and showcase

Rust was chosen for its speed, memory safety, and ability to handle large text efficiently.
This change improves UX by enabling bulk selection and copying of README content,
while also serving as a demonstration of Rust integration in the playground.

playground/rust/.gitignore

@@ -0,0 +1,25 @@
+# Generated by Cargo
+# will have compiled files and executables
+/target/
+
+# Remove Cargo.lock from gitignore if creating libraries
+Cargo.lock
+
+# These are backup files generated by rustfmt
+**/*.rs.bk
+
+# IntelliJ project files
+.idea/
+*.iml
+
+# VS Code settings
+.vscode/
+
+# Byebug
+.byebug_history
+
+# MacOS files
+.DS_Store
+
+# Node modules (if using node for frontend)
+node_modules/