[refactor] Split the 4,467-line lib.rs into domain modules - #273

Summary

• Refactored the contracts/marketx contract by splitting the single 4,467-line lib.rs into focused domain modules.
• Preserved the existing public contract surface, Contract type, exported function names, events, and types.
• Removed unused artifacts and moved coverage tooling outside the contract crate.
• Improved maintainability, reviewability, onboarding, and reduced the likelihood of merge conflicts.

Linked Issue

Closes #261

CI Checklist

Before requesting review, confirm all required checks pass locally:

• cargo fmt --all -- --check
• cargo clippy --all-targets -- -D warnings
• cargo test
• ./scripts/build_wasm.sh — blocked by the local Rust toolchain because the wasm32v1-none target is not installed.

Notes for Reviewers

Motivation

• Break up the single 4,467-line lib.rs into focused, reviewable domain modules to reduce merge conflicts and speed onboarding.
• Keep the public contract surface and single Contract type identical while moving implementation code into logical files covering escrow lifecycle, admin, fees, arbiters, milestones, group buys, time-locks, mediation, multi-arbiter voting, token controls, and utilities.
• Remove dead/unused artifacts from the contract crate and ensure coverage tooling is not compiled into the WASM.

Description

• Replaced the large contracts/marketx/src/lib.rs implementation with a compact root that declares and re-exports modules and types while retaining a single #[contract] pub struct Contract; entrypoint.

• Split the implementation into domain files under contracts/marketx/src/:

  • admin
  • arbiters
  • escrow
  • fees
  • group_buys
  • lifecycle
  • mediation
  • milestones
  • multi_arbiter
  • time_locks
  • token_controls
  • utilities

• Kept the existing errors and types modules in place.

• Moved tarpaulin.rs out of the contract crate into tools/tarpaulin.rs.

• Deleted the unused Automation.rs.

• Adjusted helper visibility to pub(crate) where required so internal modules can share implementation helpers without unnecessarily expanding the public API.

• Verified public API parity by comparing exported pub fn names before and after the refactor.

• Preserved existing events and types with no public function renames or intentional API changes.

• Commit: refactor: split contract into domain modules

Testing

• cargo fmt --all -- --check — passed.
• cargo clippy --all-targets -- -D warnings — passed with no warnings.
• cargo test — passed: 128 unit tests + 2 integration tests.
• ./scripts/build_wasm.sh — could not complete in the current environment because the wasm32v1-none Rust target is not installed. The toolchain reports E0463: can't find crate for core and indicates that rustup target add wasm32v1-none is required.

The WASM build failure appears to be an environment/toolchain setup issue rather than a compilation error in the refactored contract.