Add `span_id` attribute to Events (instrumentation) (#12417)

* add span_id to Event

* remove raise err in NullHandler

* wip

* modify root dispatcher event enclosing span

* remove *args as we have bound_args now

* add LLMChatInProgressEvent

* add LLMStructuredPredict Eventst

* store span_id before await executions

* add SpanDropEvent with err_str payload

* add event to _achat; flush current_span_id when open_spans is empty

* llm callbacks use root span_id

* add unit tests

* remove print statements

* provide context manager returning a distpatch event partial with correct span id

* move to context manager usage

* fix invocation of cm

* define and use get_dispatch_event method

* remove aim tests