Review and update existing agents

[cdummett]

Summary

Ticket is to review the structure of the Agent class and organise child classes into categories.

Updating agents

Properties which are standard to every Agent, AgentWithWallet, and StateAgentWithWallet need to be reviewed.

Categorising agents

Currently Agents are spread out though-out the code-base with the majority in vega_sim/scenario/common.py.

To improve readability, agents should be split into the following categories:

• LiquidityProviders
• MarketMakers
• Traders
• Snitches

Each category will have a separate file within an agents dir and its own class (inhering from Agent) with common properties / abstract methods for that agent category.

Updating agents should have considerations for future core features; e.g. successors, perps, and spots.

Stretch Goal

Should some agent parameters allow a list instead of a single value. Would make it easy to modify agents to exhibit behavior which varies with time rather than creating a whole new agent.

e.g. we want to gradually increase trade volume on the market, pass a list of order_size to a MarketOrderTrader rather than a fixed order_size.