Serialize eth_feeHistory block count as QUANTITY

[nlordell]

Motivation

Retrieving fee history with, say, a u64 would serialize the the block_count as a number twice, instead of first trying as a QUANTITY which is my understanding of what it is meant to do (i.e. hex-encoded string - e.g. 0x42). This PR aims to fix that.

Solution

Instead of serializing the block_count that is passed in, it first converts to a U256 (which serializes as a QUANTITY).

PR Checklist

• Added Tests (No - but should be covered by existing tests?)
• Added Documentation (No - behaviour shouldn't have been changed)
• Updated the changelog

[gakonst]

Good catch!

[nlordell]

There was an issue!