Refactor: split `contracts/escrow/src/tests.rs` into thematic modules

**Status:** Open - unassigned  
**Labels:** `cleanup`, `testing`  
**Priority:** Medium  

**Description:**  
The escrow test file is large and getting harder to navigate. Splitting by lifecycle, admin, events, and TTL would make contributor work easier.

**Tasks:**
- Break tests into smaller modules or files
- Preserve helper reuse and readability

---