Return zero tip cap if next baseFee is lower bound

[hyeonLewis]

Proposed changes

Currently, SuggestTipCap always returns tip cap based on fee history. This PR makes it return zero tip cap if nextBaseFee == LowerBoundBaseFee, which is currently 25 Gkei.

Types of changes

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• [ ] Bugfix
• [ ] New feature or enhancement
• [x] Others

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Related issues

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Further comments

// When nextBaseFee == 25 Gkei
> cast rpc eth_maxPriorityFeePerGas --rpc-url http://localhost:8551/   
> "0x0"
> cast rpc eth_gasPrice --rpc-url http://localhost:8551/                                                                  
> "0x5d21dba00" // 25 gwei

// When nextBaseFee > 25 Gkei (and intentionally sent txs with very high `effectiveGasPrice`)
> cast rpc eth_maxPriorityFeePerGas --rpc-url http://localhost:8551/
> "0x746a528800" // 500 Gkei, which is GPOMaxPrice
> cast rpc eth_gasPrice --rpc-url http://localhost:8551/                            
> "0x12309ce5400" // (500 + 750) Gkei = 1,250 Gkei