fix(ethers-core): more accurate priority fee defaults

[aroralanuk]

Motivation

@christianangelopoulos spotted us overpaying priority fees on low-cost chains because of the default minimum of 0.1 gwei.

Looking deeper into this, there's some hardcoded/unnecessary logic that doesn't suit our needs well for transaction submission on EVM chains.

Solution

Idea is to make it estimate closer to that in alloy/metamask:

• @christianangelopoulos set the EIP1559_FEE_ESTIMATION_DEFAULT_PRIORITY_FEE to 1wei if say the rewards isn't provided (bc 0 may be problematic for some chains)
• @christianangelopoulos set base_fee as 2 x last block base fee (conservative compared to metamask's 1.25x for fast mode)
• max_fee is now unconditionally priority_fee + base_fee (to not starve off base_fee)
• updated the base_fee to always be non-zero
• remove outlier rejection from median calculation (median is robust to outliers)
• 1.2x multipler for median priority fee (conservative compared to metamask which used 0.97x even for fast mode)

Tests

Unit

Note: Failing tests are etherscan API-related, not relevant for this PR.

[christianangelopoulos]

looks good to me — I like the EIP1559_PRIORITY_FEE_MULTIPLIER to ensure deliverability without too much added overhead cost