Add CircuitBreaker half-open quota replenishment scheduler

[greatest0fallt1me]

Description

circuit_breaker.rs exposes BreakerState::HalfOpen but does not throttle traffic through it: any call slips while the breaker is half-open. Add a quota-based scheduler so only N calls per minute are admitted in half-open before deciding to fully close or reopen.

Requirements and Context

• Add HalfOpenQuota { calls_per_minute: u32, evaluation_window_s: u64 } to breaker config
• Track admission counter under temporary storage
• On quota exhaustion in window, transition to Closed; on any failure, back to Open
• Must be secure, tested, and documented
• Should be efficient and easy to review

Suggested Execution

1. Fork the repo and create a branch

   git checkout -b feature/circuit-breaker-halfopen-quota

2. Implement changes
   • contracts/predictify-hybrid/src/circuit_breaker.rs
   • contracts/predictify-hybrid/src/circuit_breaker_tests.rs
3. Test and commit
   • cargo test -p predictify-hybrid halfopen_quota
   • Cover edge cases
   • Include test output and notes in the PR

Example commit message

feat: add half-open quota scheduler to CircuitBreaker

Acceptance Criteria

• Half-open admits exactly calls_per_minute calls per evaluation window
• Transitions deterministically on quota saturation
• No unwrap() in any new code path

Guidelines

• Validate auth, overflow, and storage TTL/archival
• Clear documentation and inline comments
• Timeframe: 96 hours

[samuelfrancis163-eng]

@samuelfrancis163-eng has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

I WOULD LOVE TO WORK ON THIS ISSUE BECAUSE I AM CONFIDENT THAT I CAN DELIVER EFFICIENTLY
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[aliyuHabibu]

@aliyuHabibu has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

Hi, please assign this issue to me. thank you

ℹ️ Repo Maintainers: To accept this application, review their application or assign @aliyuHabibu to this issue.

[drips-wave]

@greatest0fallt1me samuelfrancis163-eng could not be assigned to this issue because they have reached the maximum of 4 accepted assignments per organization in the current wave of the Stellar Wave Program.

The assignee has been removed. Please choose a different contributor.

[grantfox-oss]

🦊 GrantFox — @aliyuHabibu has been assigned to this issue as part of the Official Campaign campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #664)
2. Your PR will be reviewed by the Predictify-org maintainers

Good luck! Track your progress on GrantFox.

[drips-wave]

Congratulations, @aliyuHabibu! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on June 30, 2026.

🧑‍💻 @aliyuHabibu: Please resolve the issue such that the repo's maintainers have enough time to review your contribution before the due date. You'll earn Points for completing the issue on-time, which will make you eligible for a share of the Stellar Wave Program's reward pool.

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