fix: correctly interpret BaseFeePerGas as big-endian

[lyfsn]

Before the fix, blockData.BaseFeePerGas was [0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 7], and baseFeePerGas would be 3166189940082864718613269121331309980362851143201109172953918312716374638592.