[Bug]: IdGenerator in OTel plugin generates the wrong ID when called concurrently

[zhongkechen]

This method could be called concurrently so set then generate pattern may not work well in a multithreading env

Originally posted by @zhongkechen in #417

[zhongkechen]

A possible solution is using thread local object, e.g.

import contextvars
from opentelemetry.sdk.trace.id_generator import RandomIdGenerator

_forced_span_id = contextvars.ContextVar("forced_span_id", default=None)

class PluginIdGenerator(RandomIdGenerator):
    def generate_span_id(self) -> int:
        forced = _forced_span_id.get()
        if forced is not None:
            return forced
        return super().generate_span_id()