[api][runtime][python] Add minimal Event lineage

[rosemarYuan]

Linked issue: Closes #841

Related discussions:

• [Discussion] Agent observability: tracing & evaluation beyond metrics + event log #710
• [Discussion][Observability 1/2] Recording Agent Traces in the Event Log #900

Purpose of change

The Event Log currently records individual Events but does not preserve enough information to reconstruct the direct causal path between an Event, the Action it triggered, and the Events emitted by that Action.

This PR implements the minimal Event-lineage phase discussed in #710.

It adds two framework-managed fields to each Event emitted by an Action:

• upstreamEventId: the ID of the Event consumed by the emitting Action;
• upstreamActionName: the name of the Action that emitted the current Event.

Together with the existing per-occurrence Event ID, these fields are sufficient to reconstruct an InputEvent-rooted Event-Action-Event causal tree from the available Event Log records.

This PR deliberately does not implement the complete execution-tracing model proposed in #900. Run identity, concrete Action invocation identity, execution hierarchy, lifecycle, retry/replay semantics, ordering, and failure details remain part of that separate design.

A real Runtime execution was verified with the following causal path:

InputEvent(input=1)
  -> action1
  -> MiddleEvent(num=2)
  -> action2
  -> OutputEvent(output=4)

The File Event Log contained three physical Event records:

Event	upstreamEventId	upstreamActionName
_input_event	absent	absent
MiddleEvent	InputEvent ID	action1
_output_event	MiddleEvent ID	action2

Running tools/reconstruct_trace_tree.py against that Runtime log produced:

Trace Tree 1
  _input_event
    [Action: action1]
      MiddleEvent
        [Action: action2]
          _output_event

The JSON reconstruction contained one root, all three Event nodes, the two expected virtual Action edges, and no warnings.

Tests

Add e2e test to review Trace Tree python/flink_agents/e2e_tests/e2e_tests_integration/python_event_logging_test.py

API

This PR changes the default Python Event ID generation strategy from content-derived IDs to UUIDv4.

Documentation

• doc-needed
• doc-not-needed
• doc-included