Reach 100% branch coverage

[MerlinEgalite]

Right now we're at 96.08%.

[MathisGD]

Isn't there a bug in the coverage ?

https://github.com/morpho-labs/morpho-blue/blob/main/test/forge/periphery/MorphoBalanceLib.t.sol

https://github.com/morpho-labs/morpho-blue/blob/main/test/forge/SafeTransferLib.t.sol

[MathisGD]

FYI: forge coverage can't work on libraries (ref: foundry-rs/foundry#2567)

[MathisGD]

I checked quickly, and the 4 branches that are "not tested" in Morpho are the 4 callbacks. But in reality they are, so it's more a bug from forge coverage. I remember @makcandrov talking about this I think.

Then this issue is more a foundry PR

[MathisGD]

If someone want to spend some time debugging forge, feel free to reopen this PR but I'm not sure it's worth. Coverage adds limited guarantees anyway.