feat(circuit-breaker): make circuit-breaker transitions explicit

[s6pa1rta3n-lab]

Description

Closes #1378

This PR makes circuit-breaker transitions explicit, deterministic, and securely gated according to the requirements of #1378:

Changes & Invariants

• Explicit Breaker Transitions: Formalized BreakerState::Closed, BreakerState::Open, and BreakerState::HalfOpen states with explicit state transition logic.
• Deterministic Cooldown Boundaries: Added half_open_since tracking in state to ensure deterministic cooldown periods (recovery_timeout) based on ledger timestamps before probe requests count towards recovery.
• Write-Gating vs Read Availability: Enforced that write/state-mutating entrypoints are blocked while Open (require_write_allowed returns Err(Error::CBOpen)), while read entrypoints remain available (is_read_allowed returns Ok(true)).
• Access Control & Authorization: Enforced that only authorized admins can trigger emergency pause (emergency_pause, pause_with_options), request resume to HalfOpen (request_resume), or force recovery (circuit_breaker_recovery).
• Comprehensive Test Suite: All 37 circuit breaker unit and integration tests are passing cleanly without mocked assertions or auth frame collisions.

Acceptance Criteria Checklist

• Defined explicit transitions and cooldown boundaries
• Blocked unsafe operations while Open
• Kept reads/queries available while Open
• Added unit tests covering all valid/invalid transitions

Payout Routing

• EVM (Base/Arbitrum/Polygon/ETH): 0xF46C9F6d70C50BF81ef3588AB523a90a594a2F89
• Stellar: GCL6OXAMLD75BMTINA6EMRUDWK5THQUSHMYNLSNBCJAPZJHNYJTUNIBC