Feat/add ttl support

[thinktanktom]

Description

This PR implements support for Extend Footprint TTL operations as requested in #47.

Changes

I've added TTL (Time To Live) extension support across multiple layers of the API:

Low-level Operation

• Added Operations::extend_footprint_ttl() method in operation.rs
• Creates the XDR operation for extending ledger entry lifetimes
• Added comprehensive tests for the operation

High-level APIs

• Added Contract::extend_ttl() method in contract.rs

  • Provides an easy way to extend deployed contract TTLs
  • Handles transaction building, simulation, signing, and submission automatically

• Added TransactionBuilder::extend_footprint_ttl() convenience method in transaction.rs

  • Enables fluent API for building TTL extension transactions

Documentation & Examples

• Added example file examples/extend_ttl.rs demonstrating usage
• Updated README.md with TTL extension documentation
• Added inline documentation for all new methods

Testing

All tests pass:

cargo test --workspace

New tests added:

• test_extend_footprint_ttl() - Tests operation creation
• test_extend_footprint_ttl_different_values() - Tests edge cases

Usage Example

// Deploy a contract
let contract = Contract::new("path/to/contract.wasm", None)?;
let deployed = contract.deploy(&env, &mut account, None).await?;

// Extend TTL to prevent archival
deployed.extend_ttl(2_000_000, &env, &mut account).await?;

Checklist

• Added low-level operation support
• Added high-level Contract API
• Added TransactionBuilder convenience method
• Added tests
• Added example
• Updated README
• All tests pass
• Code formatted with cargo fmt
• No clippy warnings

Closes #47

[MCarlomagno]

LGTM

[merkle-maren]

Useful feature and approved 2 months ago. Who can merge it?