feat: time-lock fee-config updates

[anupam7984]

closes #630

Summary

Wraps fee-config updates in a governance time-lock to prevent surprise changes. Follows a proposal → queue → apply cycle with a mandatory delay.

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Changes

contracts/predictify-hybrid/src/fees.rs

• Added FeeConfigManager::queue_update(env, admin, new_config, eta) — stages a new config with a future ETA. Rejects past ETAs with Error::InvalidInput.
• Added FeeConfigManager::apply_update(env, admin) — activates the queued config only when env.ledger().timestamp() >= eta. Clears pending storage after application.
• Added FeeConfigManager::cancel_queued_update(env, admin) — admin-only cancel before ETA. Requires both require_auth() and validate_admin_permissions.
• Added FeeConfigManager::get_queued_fee_config(env) — returns Option<(FeeConfig, u64)> for transparency.
• Updated FeeManager::update_fee_config signature to accept eta: u64 and delegate to queue_update.
• Added FeeManager::apply_fee_update and FeeManager::cancel_fee_update public wrappers.
• No unwrap() introduced — all Option types handled with ok_or.

Tests (5):

• test_queue_update_stores_pending_config — verifies queued config is stored
• test_apply_update_before_eta_fails — apply rejected with Error::InvalidInput
• test_apply_update_at_eta_succeeds — sets timestamp, applies, verifies active config matches
• test_cancel_queued_update_removes_pending — cancel clears pending, confirmed via get_queued_fee_config
• test_queue_update_with_past_eta_fails — past ETA rejected

contracts/predictify-hybrid/src/events.rs

Added 3 event types and emit methods:

Event	Fields
FeeConfigQueuedEvent	admin, eta, all 6 FeeConfig fields, timestamp
FeeConfigAppliedEvent	admin, all 6 FeeConfig fields, timestamp
FeeConfigCancelledEvent	admin, timestamp

contracts/predictify-hybrid/src/admin.rs

Updated AdminFunctions::update_fee_config to accept eta: u64 and delegate to FeeManager::update_fee_config. Added apply_fee_update and cancel_fee_update public admin functions.

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Files Changed

File	Additions	Deletions
contracts/predictify-hybrid/src/fees.rs	+192	-17
contracts/predictify-hybrid/src/events.rs	+89	-0
contracts/predictify-hybrid/src/admin.rs	+23	-3

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Acceptance Criteria

• Apply before ETA rejected with typed error (Error::InvalidInput)
• Cancel path requires admin auth (require_auth + validate_admin_permissions)
• ETA stored and surfaced in FeeConfigQueuedEvent
• No unwrap() introduced — all Option types handled with ok_or
• env.ledger().timestamp() used for ETA comparisons

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