fix(tholos-v2): prevent initialize front-running via atomic constructor

[s6pa1rta3n-lab]

Summary

Resolves #154.

In Soroban Protocol 20+, contract deployment and initialization can be front-run if initialization is performed as a separate transaction after deployment.

This PR implements __constructor on TholosV2 in contracts/tholos-v2/src/lib.rs. Soroban invokes __constructor atomically during deployment (DeployWithConstructor on-chain / env.register(TholosV2, (admin, ...)) in test environments), guaranteeing the contract instance is configured atomically upon instantiation.

Changes

• Added pub fn __constructor(...) -> Result<(), Error> to contracts/tholos-v2/src/lib.rs delegating to Self::initialize(...).
• Updated Fixture::new() in contracts/tholos-v2/src/test.rs to register the contract with constructor parameters.
• Updated test suites and snapshots across tholos-v2.

Verification

• cargo fmt --check passed.
• cargo clippy -p tholos-v2 --all-targets -- -D warnings passed without warnings.
• cargo test -p tholos-v2 passed (108 tests).
• cargo test -p tholos passed (69 tests).
• cargo test -p compute-commitment passed.

Payout Routing

• EVM (Base/Arbitrum/Polygon/ETH): 0xF46C9F6d70C50BF81ef3588AB523a90a594a2F89
• Stellar: GCL6OXAMLD75BMTINA6EMRUDWK5THQUSHMYNLSNBCJAPZJHNYJTUNIBC

[collinsezedike]

@s6pa1rta3n-lab Closing. #154 has no assignee. Comment on the issue and wait to be assigned before opening a PR.