feat: eager init Spark wallet and add stream recovery

[TaprootFreak]

Problem

The SparkWallet is initialized lazily (only on first access). This means:

1. The SDK's internal background stream (setupBackgroundStream()) doesn't start until the wallet is first used
2. Incoming transfers are not automatically claimed until the wallet is actively accessed
3. If the background stream dies after 10 reconnect attempts, there is no recovery mechanism
4. Outgoing transfers are only considered complete after the receiver claims, blocking payouts unnecessarily

Solution

• Eager initialization: Initialize SparkWallet immediately at boot via AsyncField eager mode, so the SDK background stream starts right away and incoming transfers are automatically claimed
• Stream recovery: Register a stream:disconnected event handler that re-initializes the wallet with a fresh background stream after the SDK exhausts its 10 internal reconnect attempts
• Exponential backoff: Reconnect attempts use increasing delays (1s, 2s, 4s, ... capped at 60s) to avoid hammering the Spark API during outages
• Auto-retry on failure: If re-initialization fails, the next attempt is scheduled automatically instead of leaving the wallet permanently broken
• Logging: All disconnect, reconnect, and failure events are logged via DfxLogger for production observability
• Outgoing tx completion: Treat TRANSFER_STATUS_SENDER_KEY_TWEAKED as confirmed for outgoing transfers, since funds have already left the wallet at that point — no need to wait for the receiver to claim

Test plan

• Deploy to DEV and verify Spark wallet initializes at boot (check logs for SDK init messages)
• Send an incoming Spark transfer and verify it is auto-claimed without any prior wallet access
• Simulate stream disconnect and verify wallet re-initializes with a new background stream
• Verify reconnect logs appear with correct backoff timing
• Send an outgoing Spark transfer and verify isTxComplete returns true after SENDER_KEY_TWEAKED (without waiting for receiver claim)
• Verify getIncomingTransfers() returns incoming transfers as COMPLETED