[ENG-756] feat(daemon): UTXO performance optimizations for large-scale wallets

[pycckuu]

Summary

• Snapshot double-buffering (RwLock<Arc<UtxoState>>) eliminates 23% reader unavailability from exclusive Mutex lock during UTXO sort operations
• Mempool overlay view (UtxoStateView) replaces full UTXO set cloning with zero-copy merge iterator
• O(N×M) → O(N+M) transaction filtering via HashSet pre-build
• Incremental round-robin address scanning replaces O(N) full rescan per sync tick
• Address derivation caching: direct ChildNumber paths + pre-sorted multisig keys + versioned monitored address cache
• Fix critical sync interval default mismatch (struct Default was 10ms vs clap 10,000ms)
• Add benchmarks for address scaling, UTXO scaling, lock contention, and production-scale stress testing

Changes

• daemon/src/utxo_manager.rs: New UtxoState snapshot with HashMap + sorted Vec<(u64, WalletOutpoint)> index; UtxoStateView overlay for mempool txs; snapshot swap under brief write-lock
• daemon/src/sync_manager.rs: RPC calls without holding UTXO lock; incremental address scanning with round-robin cursor
• daemon/src/address_manager.rs: Versioned address cache (Arc<Vec<Address>>), AddressQuerySet eliminating string round-trips, cheaper derivation paths, pre-sorted multisig keys
• daemon/src/service/get_utxos.rs: Snapshot-once reads, pre-computed dust threshold, HashSet address filter
• daemon/src/service/get_balance.rs: Snapshot-based balance computation
• daemon/src/transaction_generator.rs: HashSet filter for select_utxos and more_utxos_for_merge_transaction
• daemon/src/args.rs: Shared DEFAULT_SYNC_INTERVAL_MILLIS const + validation test
• daemon/benches/: 4 benchmark files (address scaling, UTXO scaling, contention, filter performance)
• daemon/src/bin/kaswallet_stress_bench.rs: Extreme-scale synthetic benchmark (1M addresses, 10M UTXOs)

Test plan

• Run cargo build and cargo test to verify compilation and existing tests pass
• Run benchmarks: cargo bench -p kaswallet-daemon --features bench
• Run stress bench: cargo run -p kaswallet-daemon --features bench --release --bin kaswallet-stress-bench -- --i-understand --addresses 100000 --utxos 1000000
• Verify sync loop works correctly with concurrent read operations
• Test with real node at scale to confirm lock contention improvement

Closes ENG-756