feat: Pause/upgrade, batch operations, and advanced access control

[Jagadeeshftw]

Summary

Implements Contract Pause & Upgrade (#39), Batch Operations (#40), and Advanced Access Control & Role Management (#41).

#39 – Contract Pause and Upgrade Mechanism

• Pause: Global and per-function pause (admin-only), time-locked unpause, emergency pause all.
• Upgrade: Version tracking, upgrade admin, set_version with upgrade events.
• Contracts: bill_payments, insurance, savings_goals, remittance_split, family_wallet.
• Migration/rollback support remains in the data_migration crate (version checks, checksum, RollbackMetadata).

#40 – Batch Operations for Efficiency

• bill_payments: batch_pay_bills(caller, bill_ids) – atomic, validated, max 50.
• insurance: batch_pay_premiums(caller, policy_ids) – atomic.
• savings_goals: batch_add_to_goals(caller, contributions) – atomic goal contributions.
• family_wallet: batch_add_family_members(caller, members), batch_remove_family_members(caller, addresses) – atomic, with size limits.
• Batch events and input validation; all-or-nothing execution.

#41 – Advanced Access Control and Role Management

• Roles: Viewer added; hierarchy Owner > Admin > Member > Viewer; function-level checks via require_role_at_least.
• Time-based access: set_role_expiry / get_role_expiry_public; expired roles rejected.
• Audit: Access audit log for add/remove member and role change; get_access_audit(limit) (last 100 entries).
• family_wallet: Pause/unpause, upgrade admin, and version with events; Owner/Admin for pause, Owner for upgrade admin.

Breaking / API changes

• bill_payments: cancel_bill(env, bill_id) → cancel_bill(env, caller, bill_id); archive_paid_bills and bulk_cleanup_bills now return Result<u32, Error>.

Tests & pipeline

• Existing tests updated (e.g. cancel_bill caller); all workspace tests pass.
• cargo fmt, cargo clippy -- -D warnings, and cargo test --workspace --all-features pass.
• Remittance_split clippy warnings (unused vars) fixed.

[Jagadeeshftw]

@Baskarayelu Please review

[Baskarayelu]

Looks good to me!