fix: safeguard LastInterestTime against hard forks

[toteki]

Description

This will prevent the excessive (~10^20 factor) interest accrued during our hard fork of asherah testnet, where we modified LastInterestTime in genesis.

---

Author Checklist

All items are required. Please add a note to the item if the item is not applicable and
please add links to any relevant follow up issues.

I have...

• included the correct type prefix in the PR title
• added ! to the type prefix if API or client breaking change
• added appropriate labels to the PR
• targeted the correct branch (see PR Targeting)
• provided a link to the relevant issue or specification
• added a changelog entry to CHANGELOG.md
• included comments for documenting Go code
• updated the relevant documentation or specification
• reviewed "Files changed" and left comments if necessary
• confirmed all CI checks have passed

Reviewers Checklist

All items are required. Please add a note if the item is not applicable and please add
your handle next to the items reviewed if you only reviewed selected items.

I have...

• confirmed the correct type prefix in the PR title
• confirmed all author checklist items have been addressed
• reviewed state machine logic
• reviewed API design and naming
• reviewed documentation is accurate
• reviewed tests and test coverage
• manually tested (if applicable)

[codecov-commenter]

Codecov Report

Merging #1288 (2101dbf) into main (1f36d96) will increase coverage by 0.22%.
The diff coverage is 71.42%.

@@            Coverage Diff             @@
##             main    #1288      +/-   ##
==========================================
+ Coverage   51.34%   51.57%   +0.22%     
==========================================
  Files          68       68              
  Lines        6834     6852      +18     
==========================================
+ Hits         3509     3534      +25     
+ Misses       3067     3061       -6     
+ Partials      258      257       -1     

Impacted Files	Coverage Δ
x/leverage/keeper/interest.go	79.51% <71.42%> (+7.22%)	⬆️

[RafilxTenfen]

can we backport this to 2.x.x ?

[robert-zaremba]

Could you add a bit more comments? You are investigating cases which potentially are not possible. It's OK to make that check, but let's describe it for completness when these things can happen. Otherwise it's a bit confusing.... it's like checking if 2+2 > 0.

[toteki]

How it is possible that we can each such a long diff? The interest is accruing regularly.

Scenarios where time difference of a year would be possible

• If a chain halt was so long, the next block would be a year later. (This is not what I expect)
• If BlockTime behaves incorrectly (Shouldn't happen, but bugs are always possible and this one would be lethal to our users.)
• If LastInterestTime in genesis file was modified during a hard fork, and the next block would see massive interest accrue on all borrows to catch up (we suspect this just happened on Asherah-2).

Curiously, the if lastInterestTime == 0 condition in AccrueAllInterest should have protected us, but it didn't.

[toteki]

can we backport this to 2.x.x ?

Yeah (might take a few manual adjustments on the backport PR).

Also I need to add a gov proposal types to adjust interest scalar and set reserve amounts - those will be a separate PR but if we backport them rather than modifying genesis file, we could fix Asherah-2 with a binary swap + proposals instead of directly editing genesis. Might be faster to just edit the file though.