test: add comprehensive tests for custom Stellar token support

[greatest0fallt1me]

Description:

Write comprehensive test cases for custom token bet placement and payouts.

Requirements and Context:

• Must achieve minimum 95% test coverage
• Should test bet and payout with custom token
• Should test balance and transfer correctness
• Should test insufficient balance and invalid token
• Should test mixed XLM and token if both supported
• Should test approval/allowance if applicable

Suggested Execution:

1. Fork the repo and create a branch

   git checkout -b test/custom-token-support-tests

2. Implement changes

   • Write tests: src/test.rs (custom token tests with mock token)
   • Validate test coverage

3. Test and commit

   • Run tests with coverage; include test output

Example Commit Message:

test: add comprehensive tests for custom Stellar token support

Guidelines:

• Minimum 95 percent test coverage
• Clear documentation
• Timeframe: 72 hours