integrate spawn locations from tokio#7417

[hawkw]

tokio-rs/tokio#7417 adds the std::panic::Location at which a task was spawned to the TaskMeta passed to the runtime's task hooks. This was released in Tokio v1.46.0. Adding this information to the DTrace probes will make it much easier to trace individual tasks in the instrumented program.

I think it should be fine to release a new minor version that depends on Tokio v1.64+, since that's a minor release of Tokio and depending on the new tokio-dtrace will also ensure that a compatible version of Tokio is pulled in. However, we should probably document the minimum required Tokio version for each tokio-dtrace release that updates the minimum tokio dep.

[hawkw]

It would be nice to also add an example D script that traces individual tasks based on a source location argument. Maybe with user function boundary probes and #pragma D option flowindent or something?