Implement retry logic with exponential backoff and circuit breaker for all RPC calls

[Kingsman-99]

Overview

Soroban RPC calls can fail transiently. Add a resilience layer to StellarSplitClient with configurable retry logic (exponential backoff with jitter) and a circuit breaker that opens after N consecutive failures and auto-resets after a cooldown period.

Requirements

• All RPC calls in StellarSplitClient wrapped with retry logic
• RetryConfig { maxRetries: number, baseDelayMs: number, maxDelayMs: number, jitter: boolean }
• CircuitBreakerConfig { failureThreshold: number, resetTimeoutMs: number }
• Circuit breaker states: CLOSED (normal) → OPEN (failing fast) → HALF-OPEN (testing recovery)
• Emit circuit state change events via client.on('circuit:open' | 'circuit:close' | 'circuit:half-open', cb)
• Non-retryable errors (e.g. InvalidInput, Unauthorized) must bypass retry immediately
• Write tests: retry exhaustion, circuit opens after threshold, circuit resets after timeout, non-retryable errors skip retry

Acceptance Criteria

• Retry with exponential backoff + jitter on all RPC calls
• Circuit breaker with all 3 states implemented
• Non-retryable errors bypass retry
• Circuit state change events emitted
• All existing tests pass
• npm test passes with zero failures
• TypeScript compiles with zero errors
• ESLint passes with zero errors

Definition of Done

All CI checks must pass before the PR is reviewed.

[nurudeenheroic]

Hello! I'd appreciate the opportunity to work on this issue.

[levoski1]

"This issue falls within my area of expertise, and I would like to contribute a fix. Please assign it to me."

[grantfox-oss]

🦊 GrantFox — @levoski1 has been assigned to this issue as part of the Official Campaign | FWC26 campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #419)
2. Your PR will be reviewed by the Stellar-split maintainers

Good luck! Track your progress on GrantFox.