Feat: Payments Module & Fix Pre-existing Workspace Test Failures

[devIKargi]

Closes #45

Summary

Adds a standardized Payments module to the shared crate with safe token transfers, fee handling, pull-based escrow, and batch payout utilities — plus an example payments-contract demonstrating the full lifecycle. Also fixes all pre-existing test failures across the workspace, bringing the full test suite from ~80 failures to 300 passing / 0 failing.

Changes

New: Payments Module (shared/src/payments.rs — 1,388 LOC + 33 unit tests)

• safe_transfer / safe_transfer_from_contract — validated token transfers with event emission
• calculate_fee / calculate_fee_split — basis-point fee math with overflow protection
• deduct_fee — atomic fee + net split to two recipients
• create_escrow / release_escrow / refund_escrow — pull-based escrow with expiry, checks-effects-interactions pattern, state-transition guards
• multi_transfer_all / execute_multi_transfer — re-exports from batch module

New: Example Contract (contracts/payments-contract/ — 19 integration tests)

• Deposit, fee-deducted withdrawals, escrow create/release/refund, batch payouts, admin-only fee config

New: Error & Event Definitions (shared crate)

• 11 payment error codes (PaymentInvalidAmount through PaymentEscrowIdOverflow)
• 5 event topic constants (PAYMENT_TRANSFER, PAYMENT_FEE, PAYMENT_ESCROW_*)

Fixes across existing crates:

Crate	Fix
shared/test_auth	Wrap storage-touching tests in env.as_contract(); separate grant/revoke into distinct contract frames to avoid Auth, ExistingValue
shared/test_storage	Wrap all tests in env.as_contract() for instance/persistent storage access
shared/batch	Create DummyBatchContract with wrapper methods for proper auth propagation
aid-contract	Remove merge conflict artifacts, fix double-counter bug in create_aid, fix storage.rs syntax
access-control	Fix Soroban client Result unwrap assertions
upgradeability	Fix fake_hash to use correct Env, wrap auth::/storage calls in as_contract, fix shadowed variable naming
registry-contract	Set ledger timestamp in test so updated_at > 0 assertion passes
governance-contract	Fix event topic assertion (ActionExecuted, not ParameterChanged)
referral-contract	Fix reward cap value in overflow test to pass validation

Validation

• ✅ cargo check --workspace — clean, 0 warnings
• ✅ cargo test --workspace — 300 passed, 0 failed, 5 ignored (pre-existing)

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Files committed (21 files, +2,682 / -361):

 contracts/payments-contract/Cargo.toml
 contracts/payments-contract/src/lib.rs
 contracts/payments-contract/src/test.rs
 shared/src/payments.rs
 shared/src/errors.rs
 shared/src/events.rs
 shared/src/lib.rs
 shared/src/batch.rs
 shared/src/test_auth.rs
 shared/src/test_storage.rs
 contracts/access-control/src/lib.rs
 contracts/aid-contract/src/lib.rs
 contracts/aid-contract/src/storage.rs
 contracts/aid-contract/src/tests.rs
 contracts/governance-contract/src/lib.rs
 contracts/referral-contract/src/lib.rs
 contracts/registry-contract/src/lib.rs
 contracts/upgradeability/src/lib.rs
 Cargo.toml
 Cargo.lock
 .freebuff/project-id

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