feat: switch assets prorate sell amount over previous sell amount USD value

[gomesalexandre]

Description

Does what it says on the box: allows for switch assets to yield the same fiat value as previously input.
Note, this may not necessarily correspond to the buy value in fiat terms, since the buy value is after fees and the output may be very different depending on swappers.

Issue (if applicable)

closes #8376

Risk

High Risk PRs Require 2 approvals

What protocols, transaction types, wallets or contract interactions might be affected by this PR?

Low, isolated to assets switch

Testing

Test in both limit and spot:

• Input some sell amount for a given pair
• Switch assets
• Notice that the sell amount for the sell asset (i.e the previous buy asset) is the same in USD terms

Engineering

• ^

Operations

• 🏁 My feature is behind a flag and doesn't require operations testing (yet)

• ^

Screenshots (if applicable)

https://jam.dev/c/5a86cf7d-0327-4065-97cd-4dd97f946039