The solana web3 connection with Xandeum-compatible JSON-RPC endpoint (e.g., 'https://api.devnet.solana.com').
The filesystem path to check (e.g., /documents/myfile.txt).
A Promise<any> resolving to the RPC response JSON, typically including a result field
indicating existence (e.g., true or false), or null if not found.
Sends a JSON-RPC request to the Xandeum RPC endpoint to check if a file or directory exists.
This function calls the custom RPC method
isExist, which should be implemented by the backend to validate the existence of metadata (files/directories) at a given path.