[cow protocol]added atoken prices to be used where price usd isnt there

[data-cowwboy]

Description:

Use underlying token prices for aTokens where the price is not available in prices.usd. This is as per the logic we have in ethereum table.

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quick links for more information:

• README.md
• spellbook docs
• CONTRIBUTING.md

[cursor]

PR Summary

Adds fallback pricing for aTokens by using underlying token USD prices in CoW Protocol trade models across multiple chains and registers the required Aave v3 sources.

• CoW Protocol trade models (arbitrum, avalanche_c, base, bnb, gnosis, linea, polygon):
  • Add atokens_mapping and atoken_prices CTEs sourced from aave_v3_<chain>.poolconfigurator_evt_reserveinitialized and prices.usd.
  • Join atoken_prices for buy/sell tokens and coalesce with prices.usd to populate sell_price/buy_price when direct USD prices are missing.
• Sources:
  • Register aave_v3_<chain>.poolconfigurator_evt_reserveinitialized in source YAMLs for all affected chains.

^{Written by Cursor Bugbot for commit 5781239. Configure here.}