fix(fib): add type annotations and strict equality for ESLint compliance

[DeepakReddyG]

Changes

• Added n: number and : number type annotations to the fibonacci function in fib.ts to fix ESLint errors (@typescript-eslint/no-unsafe-return, @typescript-eslint/restrict-plus-operands).
• Changed == to === for strict equality checks.

Testing

• Ran npm run lint in the terminal to check for ESLint errors in fib.ts—no errors showed up.
• Tested the fibonacci function with fibonacci(5) (got 8), fibonacci(0) (got 0), and fibonacci(-1) (got -1) to make sure it works.
• Checked that fibRoute.ts still works with the updated fib.ts by testing GET /5 in my app (it returned fibonacci(5) is 8).

Fixes #1