[Feature]: Implement `From<String>` for errors

[Shatur]

Prerequisites

• I have searched existing issues to ensure this isn't a duplicate

Problem Statement

Creating erros is not very ergonomic. Even using a helper method:

    userdata
        .borrow_mut::<T>(state)
        .ok_or_else(|| runtime_error(format!("unable to downcast to `{}`", any::type_name::<T>())))

Proposed Solution

We can implement conversion from string to allow this:

    userdata
        .borrow_mut::<T>(state)
        .ok_or_else(|| format!("unable to downcast to `{}`", any::type_name::<T>()).into())

That's what Bevy does for its own types.

Alternatives Considered

No response

Additional Context

No response

Implementation

• I'm willing to implement this feature myself
• I can help with testing and feedback