PLAT-59 Feat: User PnL

[JonathanAmenechi]

This PR adds a lifetime PnL field to the Account entity and implements a new MarketProfit entity to track pnl per market per user.

Builds off earlier work done in this branch: https://github.com/Polymarket/polymarket-subgraph/tree/feat/pnl

PnL is updated on:

• FPMM Trade
• Orderbook Trade
• Merge
• Redeem