Set `blobhash(i)` within test.

[HrikB]

Add a cheatcode for setting the blobhash within a test so that it can be tested.

[DaniPopes]

You can use blobhashes: https://github.com/foundry-rs/forge-std/blob/0e7097750918380d84dd3cfdef595bee74dabb70/src/Vm.sol#L1770-L1773