fix(schema): Allow regular functions in resolvers

[ramijarrar]

Alters the expected return type of property resolvers and converters from Promise<T> to Promise<T> | T.

This ensures users are not forced to unnecessarily provide async functions with no await expression, which is often considered bad practice and disallowed by linting rules.

[daffl]

This is a really good change. Will go out with the next release!