Add Unauthorized Withdrawal Prevention Tests

[popsman01]

Description
Validate that no unauthorized actor can extract funds from reserves through public contract functions.

Motivation
This issue is required to complete the Tossd contract implementation and ensure the system behaves correctly under all conditions.

Requirements and context

• Must be secure, tested, and documented
• Should be efficient and easy to review
• Primary files: Tossd-contract/src/lib.rs

Proposed Solution
Complete the following in a focused PR off feature/unauthorized-withdrawal-tests:

• Write adversarial tests for unauthorized withdrawals
• Cover admin and non-admin callers
• Document fund safety assumptions

Technical Implementation

Files to modify:

• coinflip-contract/src/lib.rs

Implementation steps:

• Write adversarial tests for unauthorized withdrawals
• Cover admin and non-admin callers
• Document fund safety assumptions

Branch: feature/unauthorized-withdrawal-tests

Example commit message

test: add unauthorized withdrawal prevention coverage

Acceptance Criteria

• Run tests
• Cover edge cases
• Include test output and security notes

Guidelines

• Assignment required before starting
• PR description must include: Closes #150

[drips-wave]

This issue has been added to the Stellar Wave Program and is worth 200 Points.

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[petersdt]

@petersdt has applied to work on this issue as part of the Stellar Wave Program's 3rd wave.

i can help to resolve this issue

i have handled similar task as this in the past kindly assign me

ETA <= 12hrs

ℹ️ Repo Maintainers: To accept this application, review their application or assign @petersdt to this issue.