eth: handle block size max

[buck54321]

I does seem limited, but considering that a regular tx is 21,000 gas, I think it's correct.

Back to the gas estimate issue, I think this means we should place a cap on the number of inits.

More broadly, it sounds like we need to place a cap on the number of lots otherwise there will be potentially unswappable orders, however huge they'd be.

Originally posted by @chappjc in #1622 (comment)

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Just spitballin'. Either...

1. Place a cap on number of lots in the dex protocol or at the server configuration level
2. Break up large swap internally to eth, which will carry a lot of complexity especially around errors.
3. Handle it in *Core, which may end up being the easiest, implementation-wise, but it's really just an ethereum thing.

[martonp]

I'll work on this. I think the third plan of handling it in Core is the best. Each wallet can specify what their limit is and core can do the batching based on that.