fix(payment): isolate malformed mempool candidates

[Alike001]

Summary

• keep scanning an active invoice when one unrelated mempool transaction returns malformed or incomplete decoded data
• preserve error evidence while allowing another valid candidate to be detected
• keep post-expiry incomplete scans fail-closed instead of falsely expiring an invoice
• retain rpc_unavailable for provider, transport, and global RPC failures

Why

Production showed successful getblockcount, getaddresstxids, getrawmempool, and many getrawtransaction calls followed by one malformed candidate. That isolated candidate incorrectly paused all pre-expiry verification.

Verification

• npm run format:check
• npm run lint
• npm run typecheck
• npm test — 152 passed, 1 skipped
• npm run secret:check
• npm run build

Closes #33

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Project	Deployment	Actions	Updated (UTC)
zecceipt	Ready	Preview	Aug 30, 2026 12:44pm

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