Wire proptest and fuzz_test modules into the build

[mikewheeleer]

Description

proptest is declared as a dev-dependency in contracts/escrow/Cargo.toml and contracts/escrow/src/proptest.rs plus fuzz_test.rs exist, but neither is referenced from lib.rs, so no property-based tests run. Wire these modules in and ensure their generators target real entrypoints.

Requirements and context

• Scoped to TalentTrust escrow Soroban contract (contracts/escrow).
• Add #[cfg(test)] mod proptest; and #[cfg(test)] mod fuzz_test; to lib.rs (or under the test module) and fix any compilation drift.
• Property generators should exercise milestone amount arrays, deposit sequences, and release/refund orderings, asserting check_accounting_invariant never panics unexpectedly.
• Acceptance: cargo test executes the property suites; cases shrink to minimal counterexamples on failure.
• Must be secure, tested, and documented.

Suggested execution

• Fork the repo and create a branch:
  • git checkout -b test/wire-proptest-fuzz
• Implement changes:
  • contracts/escrow/src/lib.rs
  • Tests: contracts/escrow/src/proptest.rs
  • Docs: docs/escrow/fuzzing.md
  • Include rustdoc/NatSpec-style doc comments on public functions
  • Validate security assumptions (auth, overflow, fail-closed state machine, storage TTL, fee accounting)

Test and commit

• Run tests: cargo test
• Cover edge cases (unauthorized callers, double release/refund, expired approvals, fee rounding, paused state)
• Include test output and security notes in the PR

Example commit message

test(escrow): enable proptest and fuzz_test modules

Guidelines

• Minimum 95% test coverage on new/changed code
• Clear documentation
• Timeframe: 96 hours from assignment

[ZEMAD0N26]

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