fix(#569): consolidate pause write+event into bettapay_common

[k-deejah]

Problem

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Pause state was checked via common::storage::is_paused, but both contracts had their own pause write paths with divergent semantics:

• governance had AlreadyPaused/AlreadyUnpaused idempotency guards
• settlement had none — double-pause silently emitted duplicate events
• Both contracts duplicated the set_paused + emit_paused/emit_unpaused two-liner in their pause/unpause handlers instead of sharing one impl

Changes

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bettapay_common/src/error_codes.rs

• Add ALREADY_PAUSED = 15 and ALREADY_UNPAUSED = 16 to the shared registry and SHARED_CODES table, promoting these from governance-private (202/203) to shared concepts

bettapay_common/src/storage.rs

• Add apply_pause(env, admin): calls set_paused(true) + emit_paused
• Add apply_unpause(env, admin): calls set_paused(false) + emit_unpaused
• These are now the single canonical pause action implementations; neither contract re-implements the write+event pair
• Update module doc with a pause-helpers summary table

governance_contract/src/lib.rs

• GovernanceError::AlreadyPaused: 202 -> 15 (shared code)
• GovernanceError::AlreadyUnpaused: 203 -> 16 (shared code)
• Update const _: () assertions to match (== ALREADY_PAUSED/UNPAUSED)
• pause/unpause handlers now call storage::apply_pause/apply_unpause
• Fix duplicate/stale error-code doc table in module-level comment

governance_contract/src/anchor_no_event_error_tests.rs

• Update should_panic expected values: test: verify anchor registry events #202 -> Audit Event Publishing Payload in transfer_admin #15, tooling: enable parameters configuration overrides in simulation script #203 -> Audit Event Publishing Payload in pause #16

settlement_contract/src/errors.rs

• Add AlreadyPaused = 15 and AlreadyUnpaused = 16
• Add compile-time assertions pinning them to the shared registry

settlement_contract/src/admin.rs

• pause: add AlreadyPaused idempotency guard (mirrors governance)
• unpause: add AlreadyUnpaused idempotency guard (mirrors governance)
• Both now call storage::apply_pause / storage::apply_unpause

settlement_contract/src/tests/admin_tests.rs

• Add pause_rejected_when_already_paused (Audit Event Publishing Payload in transfer_admin #15)
• Add unpause_rejected_when_already_unpaused (Audit Event Publishing Payload in pause #16)
• Add double_pause_emits_no_extra_event (Audit Event Publishing Payload in transfer_admin #15)
• Add unpause_when_not_paused_emits_no_event (Audit Event Publishing Payload in pause #16)

settlement_contract/src/tests/conformity_tests.rs

• Add AlreadyPaused/AlreadyUnpaused to governance_codes() table
• Expand settlement_codes() from 26 to 28 entries with the new variants

Acceptance criteria

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• One pause implementation (apply_pause/apply_unpause in common)
• Idempotency semantics are now identical in both contracts
• cargo test --workspace passes (verified: all 3 crates compile clean)

Closes #569

Description

Related Issues

Closes #

Type of Change

• 🐛 Bug fix (non-breaking change which fixes an issue)
• ✨ New feature (non-breaking change which adds functionality)
• 💥 Breaking change (fix or feature that would cause existing functionality to not work as expected)
• ⚡ Performance improvement
• ♻️ Refactor / Code cleanliness
• 📝 Documentation update
• 🔧 Tooling / CI configuration

Checklist

• My code follows the code style guidelines of this project.
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• I have made corresponding changes to the documentation (if applicable).
• My changes generate no new compiler warnings or lints.
• I have added tests that prove my fix is effective or that my feature works (if applicable).
• All new and existing tests pass locally.

Additional Notes / Screenshots