[Test] Add MockBcForgeClient, property-based tests, and test scaffold…

[Ceejaytech25]

[Test] Add Mock SDK, E2E, Property-Based, and Fuzz Testing

Summary

This PR implements the following test-related enhancements:

1. Mock SDK Client (#94)

• Adds MockBcForgeClient to the SDK.
• Provides an in-memory mock for frontend developers to test logic without a live Soroban RPC.
• Supports mint, transfer, approve, transferFrom, and allowance logic.

2. Property-Based Testing (#96)

• Integrates the proptest crate in the token contract.
• Adds property-based tests for minting, transferring, and burning tokens.
• Verifies supply invariants and edge cases for arithmetic operations.

3. E2E Testing with Stellar Local Sandbox (#95)

• Adds scaffolding for end-to-end tests using a local Stellar network.
• Prepares for contract + SDK integration tests with stellar-cli local network.

4. Fuzz Testing for Core Token Logic (#97)

• Adds fuzzing scenarios for the token contract state machine.
• Targets panic conditions and edge cases using property-based and fuzz tests.

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All changes are on branch: test/mock-e2e-fuzz-proptest

Closes #94
Closes #95
Closes #96
Closes #97

[Ceejaytech25]

@p3ris0n , pls review PR

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