Depth Chart centre line and steps seem incorrect.

[bwallacee]

Description

market: https://vegafairground.eth.limo/#/markets/cc8b1b2964d0ac108a67e2e6ad237ad1c5fcd3083dedc6bc291d285f43211bd2

The two sides don't meet in the middle:

I believe this is causing the issue below:

If you hover over the top of short side you can see that the long side has added an invisible flat step.

If you hover over the top of the long side. You can see that the short side is one step lower:

Acceptance Criteria

• [ ] The mid price on the chart should always be the midpoint of the best bid and best ask
• [ ] This should be true even if the market decimals of the market
• [ ] We should interpolate between best bid / best ask