Fix/pausability invariants concurrency verification

[Mosas2000]

Summary
This pull request addresses and resolves four open issues across the Soroban smart contracts and Node/TypeScript backend in YieldVault-RWA:

#960: Implement role-restricted pausability controls allowing a designated Pauser address alongside Admin.
#959: Add unit and property-based invariant test coverage asserting share-price monotonicity ($P_{t+1} \ge P_t$).
#957: Introduce optimistic concurrency controls (OCC) in the backend persistence layer.
#968: Add formal verification specifications and executable invariant tests for critical accounting logic.
Issue Breakdowns & Changes Implemented

1. Contract: Implement pausability controls with role-restricted access #960 Contract: Implement pausability controls with role-restricted access
   Role Assignment: Added DataKey::Pauser in DataKey enum and implemented set_pauser(env, pauser) (admin-only) and pauser(env) query.
   Role-Restricted Execution: Added pause_with_role(env, caller, reason) and unpause_with_role(env, caller) functions enforcing authorization via permissions::require_pauser_or_admin_auth.
   Test Coverage: Added test_role_restricted_pausability_controls in contracts/vault/src/feature_tests.rs.
2. Contract: Add invariant tests for share-price monotonicity #959 Contract: Add invariant tests for share-price monotonicity
   Vault Invariant Suite: Added test_invariant_share_price_monotonicity_under_yield_accrual and test_invariant_share_price_monotonicity_under_deposits_and_withdrawals in contracts/vault/src/invariant_tests.rs.
   Math Fuzz Assertions: Extended contracts/share-price-math/src/fuzz_invariants.rs to assert $P_{after} \ge P_{before}$ across arbitrary positive yield accruals.
3. Backend: Introduce optimistic concurrency controls in persistence layer #957 Backend: Introduce optimistic concurrency controls in persistence layer
   Schema Extensions: Added version Int @default(1) column to stateful models (VaultState, BulkExportJob, WebhookEndpoint, EmailQueue, TransactionBackfillJob) in backend/prisma/schema.prisma.
   OCC Handler & Retries: Implemented OptimisticConcurrencyError, assertVersionMatch, and executeWithOptimisticConcurrency with exponential backoff and randomized jitter in backend/src/optimisticConcurrency.ts.
   Test Coverage: Created backend/src/tests/optimisticConcurrency.test.ts covering version matching, collision detection, and retry bounds.
4. Contract: Add formal verification notes for critical accounting logic #968 Contract: Add formal verification notes for critical accounting logic
   Mathematical Specification: Created docs/FORMAL_VERIFICATION_ACCOUNTING.md documenting formal theorems for share conversion, share-price monotonicity, solvency bounds, and round-trip loss invariants.
   Executable Formal Property Suite: Created contracts/vault/src/formal_verification_tests.rs verifying Theorems 1–3 in Soroban contract tests.
   Architecture References: Updated docs/CONTRACTS_ARCHITECTURE.md to index formal verification notes.
   Related Issues
   Closes Contract: Implement pausability controls with role-restricted access #960
   Closes Contract: Add invariant tests for share-price monotonicity #959
   Closes Backend: Introduce optimistic concurrency controls in persistence layer #957
   Closes Contract: Add formal verification notes for critical accounting logic #968

[drips-wave]

@Mosas2000 Great news! 🎉 Based on an automated assessment of this PR, the linked Wave issue(s) no longer count against your application limits.

You can now already apply to more issues while waiting for a review of this PR. Keep up the great work! 🚀

Learn more about application limits