Fixed parsing of buy and sell amounts in pricing

[naddison36]

Summary

• Treat --buy-amount and --sell-amount as token-denominated values across the WETH, Ethena, and USDC pricing actions
• Scale buy amounts using the liquidity asset’s decimals and sell amounts using the base asset’s decimals
• Support fractional amounts, such as 1.5
• Update action parameter types and documentation
• Add regression coverage for 18-decimal and 6-decimal assets

Testing

• Added tests covering:
  • 1 token with 18 decimals
  • 1 token with 6 decimals
  • 1.5 tokens with 6 decimals
• Prettier and git diff --check pass