feat(solutions): add fibonacci/rust/function

challenges/fibonacci/solutions/rust/function/Cargo.lock

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+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "rust_application"
+version = "1.0.0"

challenges/fibonacci/solutions/rust/function/Cargo.toml

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+[package]
+name = "rust_application"
+version = "1.0.0"
+edition = "2021"
+
+[dependencies]

challenges/fibonacci/solutions/rust/function/README.md

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+# fibonacci/rust/function
+
+Created by [@Divlo](https://github.com/Divlo) on 5 January 2023.

challenges/fibonacci/solutions/rust/function/src/main.rs

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+use std::io;
+
+pub fn fibonacci(number: u32) -> u32 {
+    if number == 0 || number == 1 {
+        return number;
+    }
+    return fibonacci(number - 1) + fibonacci(number - 2);
+}
+
+fn main() {
+    let mut number = String::new();
+    io::stdin()
+        .read_line(&mut number)
+        .expect("Failed to read `stdin` line.");
+    let number: u32 = number
+        .trim()
+        .parse()
+        .expect("Failed to convert `number` as an `u32`.");
+    println!("{}", fibonacci(number));
+}