fix(solana): handle Helius mixed parsed/base64 responses and Meteora position width errors

[fengtality]

Summary

This PR fixes two critical issues with Solana token account handling and Meteora position creation:

1. StructError from Helius mixed responses - When Helius RPC returns token accounts with mixed parsed/base64 data, the Solana web3.js library throws a StructError during validation
2. Meteora InvalidPositionWidth error handling - Position width constraint violations now return clear error messages to users

Changes

Helius Mixed Response Handling

• Added fetchTokenAccountsBase64() fallback method that uses base64 encoding exclusively
• Updated fetchTokenAccounts() to catch StructError and fall back to base64 encoding
• Updated deprecated getBalance() method to handle mixed responses
• Ensures compatibility with Helius RPC's occasional base64 fallback for unparseable token accounts

Meteora Position Width Error Handling

• Added specific error handler for InvalidPositionWidth (error code 6040/0x1798)
• Returns clear message: "Error Code: InvalidPositionWidth. Error Number: 6040. Error Message: Invalid position width. Please use a position width of 69 bins or lower."
• Fixed Meteora openPosition route to preserve actual error messages instead of generic "Request failed"

Code Quality Improvements

• Removed balance validation from Meteora openPosition to align with PancakeSwap-Sol behavior
• Balance checks now happen at transaction execution time (cleaner approach)
• Avoids deprecated getBalance() method in connector code

Test Plan

• Tested Meteora position opening with valid narrow range (120-170) - succeeds
• Tested Meteora position opening with invalid wide range (100-200) - returns proper error message
• Verified quote-position endpoint still works correctly
• Confirmed StructError no longer occurs with Helius RPC

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