Verify order executed amount in settlement encoder

[vkgnosis]

Fixes #163

@josojo wrote

I think we should make sure that the for a partially fillable order the "executed amount <= sell amount" and for a killorfill order "executed amount== sell_amount".

But I think for buy orders the executed amount refers to the buy amount.

Test Plan

Adapted the existing tests which showed that the verification worked

[MartinquaXD]

I think those conditions can be even stricter since partially fillable orders could already be partially filled.
executed_amount <= (order.creation.sell_amount - order.metadata.executed_sell_amount)

[vkgnosis]

You're right. I was thinking this would be detected during simulation because the contract enforces it too but it probably makes sense to catch it as early as possible.

[vkgnosis]

This was a bit annoying because the other number is a BigInt so would have to convert and then decide what to do if that value doesn't make sense like saturating sub so I left it out for now. Will think again how I want to do this.

[vkgnosis]

@josojo could you review this since you made the original issue? Also the part I quote in the description.

[josojo]

Yes, great. Pr looks good. Thanks for modifying it for buy orders. Makes sense to me for sure.

[codecov-commenter]

Codecov Report

Merging #164 (6e0a624) into main (1738304) will increase coverage by 0.01%.
The diff coverage is 91.66%.

❗ Current head 6e0a624 differs from pull request most recent head b4fe284. Consider uploading reports for the commit b4fe284 to get more accurate results

@@            Coverage Diff             @@
##             main     #164      +/-   ##
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+ Coverage   64.82%   64.84%   +0.01%     
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  Files         185      185              
  Lines       38393    38386       -7     
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+ Hits        24888    24890       +2     
+ Misses      13505    13496       -9