feat(cntr): add validator crate — closes #1024, #1028, #1031, #1036

[authenticeasy-sys]

Summary

Creates the contracts/cntr crate with four new modules resolving CT-07, CT-11, CT-14, and CT-19.

Changes

contracts/cntr/src/credit_topup.rs — closes #1024

• validate_topup(current_balance, topup_amount, max_balance) -> Result<i128, &'static str>
• Rejects zero/negative top-ups, guards against overflow, enforces max balance
• 7 unit tests including exact boundary, one-above-max, overflow guard

contracts/cntr/src/multi_booking.rs — closes #1028

• get_booking_limit(tier) -> u32: Bronze=2, Silver=5, Gold=10, Platinum=u32::MAX, unknown→Bronze
• can_make_booking(tier, current_active_bookings) -> bool
• 8 unit tests covering all tiers, unknown tier, at-limit and below-limit cases

contracts/cntr/src/payment_validator.rs — closes #1031

• validate_payment_amount(received, expected, tolerance) -> Result<(), &'static str>
• Validates expected > 0, checks received >= expected - tolerance
• 7 unit tests: exact, within tolerance, one-below-tolerance, overpayment, zero/negative expected

contracts/cntr/src/role_checker.rs + contracts/cntr/tests/access_control_tests.rs — closes #1036

• RoleRegistry: in-memory role store with grant_role, revoke_role, has_role, get_roles
• 12 integration tests: grant, idempotent grant, multi-role, revoke, revoke-nonexistent (no panic), unknown address, empty registry, independence across addresses

contracts/Cargo.toml

• Added cntr to workspace members so CI picks it up

Tested

All tests verified locally via cargo test -p cntr.

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[yusuftomilola]

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