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/pub/pub.go

@@ -67,7 +67,7 @@ func packageDescriptorToMetadata(baseURL string, pd *packages_model.PackageDescr
 		Version:    pd.Version.Version,
 		ArchiveURL: fmt.Sprintf("%s/files/%s.tar.gz", baseURL, url.PathEscape(pd.Version.Version)),
 		Published:  pd.Version.CreatedUnix.AsLocalTime(),
-		Pubspec:    pd.Metadata.(*pub_module.Metadata).Pubspec,
+		Pubspec:    packages_model.DescriptorMetadata[*pub_module.Metadata](pd).Pubspec,
 	}
 }