feat: add stellar examples

[dylankilkenny]

Summary

• Added practical Stellar examples for common operations:
  • sendPayment.ts - Native XLM and asset transfers
  • uploadWasm.ts - Smart contract WASM upload
  • createContract.ts - Contract deployment from WASM
  • invokeContract.ts - Contract function calls with typed arguments
• Custom Type Definitions: Added stellar-transaction-request.ts model with proper TypeScript types for Stellar's unique data structures (ScVal, auth specs, asset types)

Testing Process

Checklist

• Add a reference to related issues in the PR description.
• Add unit tests if applicable.
• Add the changeset file. (run npx changeset add)