test(aid_escrow): add proptest invariant fuzz tests (#223) (#407)

* test(aid_escrow): add invariant fuzz tests with proptest (#223)

- Add proptest-driven fuzzer covering Fund, CreatePackage, Claim,
  Disburse, Revoke, Refund, and WithdrawSurplus operations
- Conservation invariant: mirror_funded == balance + mirror_withdrawn
- Solvency invariant: balance >= locked funds at every step
- Non-negativity invariant: no account goes below zero
- Post-hoc event cross-check on final transaction
- 7 deterministic smoke tests + 1 randomized proptest (100 cases)

* fix(ci): increase fetch depth for Cargo.lock check to resolve merge base in cross-fork PRs

* fix(ci): use two-dot diff for Cargo.lock check to avoid merge base requirement in shallow clones

* style(onchain): apply rustfmt to invariant tests

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Co-authored-by: dzekojohn4 <dzekojohn4@users.noreply.github.com>

Author: dzekojohn4