[feature] THORFi Lending #check-lint-warning

This adds the open/close loan logic.

Code walkthrough https://www.youtube.com/watch?v=8qCiyLy4YEw

NOTE Min Out for opening or closing the loan is non-functional in this PR. Adding this functionality seems more complicated than the loan logic alone and therefore seemed appropriate to put it into a separate PR.

ADD-ON 1 added logic to check rune supply on opening loans. This is to ensure that new loans cannot be opened if we're at the max supply of rune (part of the circuit breaker).

ADD-ON 2 added two endpoints to get a specific borrower from a given pool, or all borrowers.