feat: Implement robust Soroban RPC Client with retry logic (#149)

[edehvictor]

Overview

This PR implements a server-side Soroban RPC client utility to allow the application to interact with the Stellar network. It provides a robust foundation for reading contract state and building transactions.

Changes Made

• Client Implementation: Created lib/soroban/client.ts as a singleton to manage the connection to the Soroban RPC node.
• Resilience: Added a withRetry helper that uses AbortController to handle request timeouts (10s) and automatic retries for transient network errors.
• Health Check: Implemented a new API route at /api/health/soroban that returns the current ledger sequence to verify connectivity.
• Documentation: Updated README.md to include environment variable configurations for both Testnet and Mainnet.

Technical Details

• Used the SorobanRpc.Server class from @stellar/stellar-sdk.
• Ensured the client is server-side only by omitting the NEXT_PUBLIC_ prefix on sensitive environment variables.

Verification

• Connection initialized with Testnet defaults.
• Error handling verified through custom SorobanClientError class.

Closes #149

[edehvictor]

@Baskarayelu, please review

[Baskarayelu]

resolve the conflicts

[edehvictor]

@Baskarayelu, I have resolved conflict. Pls kindly review

[Baskarayelu]

LGTM!