Improve context guard extraction failure handler

[erichulburd]

Currently there are configurable handlers for context guard extraction:

pyo3-opentelemetry/crates/opentelemetry-macros/src/lib.rs

Line 211 in c8bcaa7

let error_handler: proc_macro2::TokenStream = match config.on_context_extraction_failure {

Rather than manually curate a set of handlers, we should enable the caller to define a callback:

fn handler(e: PyErr) -> PyResult<()>

If handler returns an error, the function is exited; otherwise it carries on.