Rename EventSerializers to AgentEventSerializers

[mssalvatore]

Refactor

Component(s) to be refactored

• event_serializers
• EventSerializerRegistry
• IEventSerializer
• PydanticEventSerializer

Explanation

The Island handles both Island events and Agent events. To avoid confusion, rename event serializer components to include "agent" in their names. Don't forget to also rename the unit test files.

Tasks

• Rename IEventSerializer to IAgentEventSerializer (0d)
• Rename EventSerializerRegistry to AgentEventSerializerRegistry (0d)
• Rename PydanticEventSerializer to PydanticAgentEventSerializer (0d)
• Rename event_serializers package to agent_event_serializers (0d)