Invoice Batch Processor with Concurrency Limiter

[Kingsman-99]

Description

When an integration needs to process dozens of invoices simultaneously (e.g. month-end batch billing), running all submissions concurrently overwhelms Horizon's rate limits and produces cascading 429 errors. The SDK must provide a batch processor that submits invoices with a configurable concurrency ceiling, respects rate-limit backoff signals, and reports per-invoice results as they settle rather than waiting for the entire batch.

Technical Context

Add src/invoiceBatchProcessor.ts. Extends src/requestBatcher.ts patterns. Uses a semaphore pattern (configurable maxConcurrent, default 3) wrapping src/client.ts submitPayment(). Integrates with src/rateLimiter.ts to detect and honour Retry-After headers. Emits batchInvoiceSettled and batchInvoiceFailed via src/events.ts. Returns AsyncIterableIterator<BatchInvoiceResult>.

Acceptance Criteria

• InvoiceBatchProcessor.process(invoiceIds: string[], config): AsyncIterableIterator<BatchInvoiceResult> yields results as each invoice settles
• No more than maxConcurrent invoice submissions are in-flight simultaneously
• On 429 response from Horizon, pauses all in-flight submissions for the duration specified in Retry-After and resumes
• BatchInvoiceResult includes invoiceId, status: 'success' | 'failed', txHash?, and error?
• Failed invoices are reported individually without aborting the rest of the batch
• All CI checks (npm test, npm run build, ESLint/TypeScript) pass and the branch has no merge conflicts

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[neyij]

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hi, i would like to work on this.

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[Dubemtopsite]

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Good day

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[Zalgia-Saga]

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I will like to work on this.

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