sdk-bedrock: InvokeFlow spans show the flow id as the agent name #195

Bedrock InvokeFlow spans get the agent name invoke_flow <flow id> (or invoke_flow unknown) in both SDKs.

The flow span is a type: "agent" span named invoke_flow ${flowIdentifier} (packages/bedrock/src/agent-handlers.ts flowName, sdks/python-bedrock/src/telemetry_dev_bedrock/_registry.py _flow_name) with only agentId set. An agent span without an agent name takes its span name, so the flow id, prefixed with the operation, shows as the agent in the Sessions Agent column, the usage breakdown by agent, and runaway-alert grouping. Python has done this since it added the default; TypeScript does it since #193, which made the two match. Spans named invoke_agent or invoke_agent <id> already get no name.

expected:

• an InvokeFlow span carries no gen_ai.agent.name, or a name that is not built from the operation and the id, in both SDKs
• the TS and Python Bedrock flow tests assert it