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>

routers/api/packages/cran/cran.go

@@ -93,7 +93,7 @@ func enumeratePackages(ctx *context.Context, format string, opts *cran_model.Sea
 			}
 		}
 
-		metadata := pd.Metadata.(*cran_module.Metadata)
+		metadata := packages_model.DescriptorMetadata[*cran_module.Metadata](pd)
 
 		fmt.Fprintln(w, "Package:", pd.Package.Name)
 		fmt.Fprintln(w, "Version:", pd.Version.Version)