Fix callback types

[nmay231]

As discussed in Discord, this changes all callback types from methods to function attributes ({ callback(a: A): T } => { callback: (a: A) => T }). This prevents type variance bugs, such as the following where the real type of onChange is (value: string | null) => void.

export default function App() {
  function expectsAString(value: string) {
    // null error is only caught at runtime, currently
    console.log(value.length); // TypeError: Cannot read properties of null (reading 'length')
  }

  return (
      <Select
        onChange={expectsAString}
        data={["React", "Vue", "Angular"]}
        clearable
      />
  );
}

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Also synchronized .nvmrc and .tool-versions.

[rtivital]

Thanks!

[nmay231]

And thank you!