Issue #217: Implement Cross-Contract Call Mocking

[Tijesunimi004]

Description

This PR addresses Issue #217 by implementing the ability to mock cross-contract calls during CLI debugging sessions. It adds the infrastructure necessary to intercept host execution calls, return pre-configured mocked values, and track invocation counts.

Key Changes

• CLI Arguments (src/cli/args.rs):
  • Added support for a repeatable --mock flag to parse CONTRACT_ID.function_name=return_value formatted arguments.
• Host Execution Inteception (src/runtime/mocking.rs & src/runtime/executor.rs):
  • Implemented MockRegistry to store specifications and track mocked executions.
  • Introduced MockContractDispatcher to handle intercepted cross-contract calls.
  • Configured the ContractExecutor to install mock dispatchers via the Soroban host environment prior to execution.
• Reporting (src/cli/commands.rs):
  • Updated the reporting layer to display a clean summary of what functions were mocked, how many arguments they received, and what they returned.
  • Displays clear warnings for unmocked cross-contract calls on mocked contracts.

Testing

• Added comprehensive unit tests validating mocked resolution and logging for unmocked requests.
• Ran cargo fmt and cargo test to ensure stability and style compliance.

Related Issues

Closes #217