fix: swap volume calculations

[dib542]

There are some issues with the current swap volume calculations:

• Fees may be incorrectly calculated from incorrect Fee keys from the Dex

  • resolution: add better restrictions on Fee values accepted, fees on tranches are not valid

• Where Fees are null the calculated fee volume may return null instead of 0

  • resolution: set null values to 0 in calculations

• Volume currently includes token reserves placed in tranches without any swap execution

  • resolution: track volume by the swapped tokens out of limit orders, which better represent executed volume