feat(agents): extend bee start event

[Tomas2D]

Extends the Bee 'start' event to allow on-fly modifications.

Usage:

const agent = new BeeAgent(...)

agent.emitter.on("start", async ({ memory, tools, meta }) => {
  console.log(`Iteration: ${meta.iteration}`);
  const lastMessage = memory.messages.at(-1);
  if (lastMessage?.text.includes("weather")) {
    tools.splice(0, Infinity, ...tools.filter((tool) => tool.name.includes("weather")));
  }
});

Ref: #184