feat(indexer): batch state sync

[m-kus]

Optimize discovery with batched RPC calls

This PR improves the efficiency of privacy pool discovery by implementing batched RPC calls for notes and channel information. Key improvements:

• Replace sequential note scanning with a two-phase approach:

  1. Batched exponential probing to find the last existing note index
  2. Efficient linear batch scanning for note amounts and nullifiers

• Add batch methods to IViews trait:

  • get_channel_info_batch: fetch multiple channels in one call
  • get_notes_batch: check existence of multiple notes
  • get_note_and_nullifier_batch: fetch note amounts and nullifier status

• Implement consume_up_to in IoBudget to handle batch operations efficiently

• Replace tokio::task::JoinSet with futures::FuturesUnordered for concurrent processing

• Clarify cursor semantics for max_note_index in incoming channels

These changes significantly reduce RPC round trips, improving discovery performance while maintaining the same functionality.

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This change is

[m-kus]

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• feat(indexer): e2e discovery flow #440
• feat(indexer): preflight endpoint, sync with abstract discovery provider interface #439
• feat(indexer): outgoing state sync endpoint #438
• feat(indexer): batch state sync #435 👈 (View in Graphite)
• feat(indexer): sync outgoing state #433
• feat(indexer): discover outgoing channels #430
• feat(indexer): find last used note index #429
• feat(indexer): outgoing channel primitives #424
• feat(indexer): filter out spent notes, use secret felt #422
• feat: scaffold e2e testing harness, move devnet dump generation to a separate script #421
• feat(indexer): sync code and spec, update guidelines and todos #414
• feat(indexer): add incoming state sync endpoint #413
• feat(indexer): api error types #412
• refactor(indexer): common helpers for spawning devnet/indexer #411
• feat(indexer): incoming state sync orchestration #410
• feat(indexer): cursor pagination for discovery #408
• refactor(indexer): reorganize discovery-core, prepare for state sync #407 : 1 other dependent PR (#453 )
• feat(ci): speed up rust workflow #415
• main

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