forbid as_u* method calls in linting

[eagr]

Closes #841

Description

Add custom lint to forbid certain as_*() conversions to avoid accidental panics.

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Other (please describe): linting

[sam0x17]

ok this looks great, if you could please instead make a PR into devnet-ready that would be great.

unfortunately github doesn't allow specifying a default branch for PRs that is different from default branch for clones

edit: I went ahead and changed base but there are now merge conflicts you will need to fix so might be preferable to just reset and stage your changes on top of current devnet-ready and commit that and force push

[eagr]

lmk if you need a hand on other issues :)

[sam0x17]

just one clippy failure and then should be good to review+merge @eagr =)

[sam0x17]

and now cargo fmt ;)

[eagr]

have been away from rust for a while. I have the commands set up again, it will be smoother next time :))