feat(maple): add pool cash balance and withdrawal queue depth monitoring

[spalen0]

Summary

• Adds check_pool_liquidity() function that queries USDC balance of pool contract, locked liquidity, and withdrawal queue depth in a single batched call
• Alerts on four conditions: low cash balance (<$1M), low cash ratio (<0.5% of TVL), high queue depth (>50 pending requests), and locked liquidity exceeding available cash (critical)
• Reuses existing WithdrawalManagerQueue ABI which already includes lockedLiquidity() and queue() functions

Test plan

• Verify batched calls decode correctly (especially queue() returning two uint128 values)
• Confirm alerts fire with current on-chain state (~$280K cash, 0.016% ratio)
• Verify no duplicate alerts when both cash balance and cash ratio thresholds are breached (uses elif)
• Run python maple/main.py against mainnet to validate end-to-end

Closes #171

🤖 Generated with Claude Code

[spalen0]

cash reserves are low:

[2026-03-17 20:15:40,866] INFO maple: Strategy allocations — Aave: $156.17M, Sky: $600.32M | Withdrawal queue: $133.40K (liquid: $756.49M)
[2026-03-17 20:15:41,053] INFO maple: Pool liquidity — Cash: $133.41K (0.007% of TVL), Locked: $0.00, Queue depth: 1 pending
[2026-03-17 20:15:41,053] DEBUG utils.telegram: Sending telegram message:
⚠️ *Maple syrupUSDC Low Pool Cash*
💵 Cash: $133.41K (threshold: $1.00M)
📊 Cash ratio: 0.007% of $1.79B TVL
🔗 [syrupUSDC Pool](https://etherscan.io/address/0x80ac24aA929eaF5013f6436cdA2a7ba190f5Cc0b)