feat: improve btcli liquidity add logic

[DeborahOlaboye]

Implements enhanced liquidity add workflow.

Description

• Validates subnet existence early
• Fetches current subnet price
• Provides conditional prompts based on price range:
  • Alpha-only when price_low >= current_price
  • TAO-only when price_high <= current_price
  • Both tokens with max liquidity calculation otherwise
• Displays available balances and max providable amounts
• Validates requested amounts don't exceed available

Includes comprehensive unit tests for new utility functions.

Closes #532

Contribution by Gittensor, learn more at https://gittensor.io/

[ibraheem-abe]

Thanks for your contribution

Currently liquidity is disabled in Bittensor and the whole system is expecting a major update which will change how liquidity looks like. I am expecting for this to get outdated.

Keeping it as a draft for now if that is not the case.