chore: enable forcetypeassert linter, fix issues (#38804)

Enable [`forcetypeassert`](https://github.com/gostaticanalysis/forcetypeassert)
linter to prevent unchecked type assertions. ~650 issues fixed, most
fixes were clean, some use `setting.PanicInDevOrTesting`.

The only behaviour changes are where code would previously send a 500 error
or panic, a 4xx error is now emitted.

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

services/packages/cargo/index.go

@@ -162,7 +162,7 @@ func BuildPackageIndex(ctx context.Context, p *packages_model.Package) (*bytes.B
 
 	var b bytes.Buffer
 	for _, pd := range pds {
-		metadata := pd.Metadata.(*cargo_module.Metadata)
+		metadata := packages_model.DescriptorMetadata[*cargo_module.Metadata](pd)
 
 		dependencies := metadata.Dependencies
 		if dependencies == nil {