Provide syntactic sugar to attach a context then automatically detach after an operation

[fractalwrench]

Similar to #4 it would be nice to create syntactic sugar that attaches a Context and then detaches it after performing an operation. Rather than using AutoCloseable it would be preferable to create a custom function on the Context interface.

Currently, this would be required to perform the operation:

fun example(ctx: Context) {
    // set 'ctx' as the implicit context
    val scope: Scope = ctx.attach()

    // span has 'ctx' set as its parent via implicit context
    tracer.createSpan("my_span")

    // unset 'ctx' and restore the previous implicit context.
    scope.detach()
}

Whereas I think we should aim for an API with fewer moving parts from a library consumer's perspective, similar to this:

fun example(ctx: Context) {
    ctx.asImplicitContext {
        tracer.createSpan("my_span")
    }
}