Improve typehint on Attributes

[nandi95]

Update type to specify value type so getAttributes().myKey will correctly typehint and not be unknown

Already started the work but is is still causing issues because of the model index signature:

export type Attributes<
    M extends HasAttributes = HasAttributes
    // string index falls back to the model index signature
> = { [P in keyof M extends AttributeKeys<M> ? keyof M : never]: M[P] };


export type KeysNotMatching<T, V> = KeysNotMatching2<keyof T, T, V>;
// Using this intermediate type to force distribution.
type KeysNotMatching2<Keys extends keyof T, T, V> = Keys extends unknown ? KeyIsAttribute<Keys, T, V> : never;
type KeyIsAttribute<Key extends keyof T, T, V> = T[Key] extends V ? never : Key;

[nandi95]

Resolved by #178