feat(sdk): implement complete deposit flow with transaction lifecycle…

[Litezy]

🚀 Overview

This PR implements the full end-to-end deposit flow in the SDK, covering everything from note generation to transaction confirmation and receipt parsing.

It provides a clean, production-ready abstraction for interacting with the deposit contract.

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✅ What’s Included

Closes #10

Core Features

• deposit() – orchestrates the full deposit lifecycle
• buildDepositTransaction() – constructs unsigned transaction
• submitTransaction() – submits + polls until confirmation
• parseDepositReceipt() – extracts leaf index + Merkle root from result
• estimateDepositCost() – estimates gas via simulation

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Flow Implementation

1. Generate a new privacy note
2. Compute commitment
3. Build deposit transaction
4. Sign transaction (via injected signer)
5. Submit to network
6. Wait for confirmation (with retry + timeout handling)
7. Parse receipt (leaf index, tx hash, root)

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Reliability & Error Handling

• Simulation failure handling
• Transaction failure detection
• Timeout handling for pending txs
• Retry logic with exponential backoff
• Contract error mapping (e.g. insufficient balance, pool paused, tree full)

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Testing

• ✅ Transaction building
• ✅ Receipt parsing
• ✅ Error scenarios (simulation + submission failures)
• ✅ Gas estimation
• ✅ Mock contract deposit flow
• ⚙️ Optional testnet integration

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📦 Developer Experience

• Fully typed TypeScript API
• Modular functions for flexibility
• Clear separation of concerns (build / submit / parse)
• SDK-safe abstractions (handles Soroban inconsistencies internally)

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📖 Example Usage

await deposit({
  server,
  signer,
  contractId,
  amount,
});