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/context/context_template.go

@@ -29,11 +29,11 @@ func NewTemplateContext(ctx context.Context, req *http.Request) TemplateContext
 }
 
 func (c TemplateContext) req() *http.Request {
-	return c["_req"].(*http.Request)
+	return c["_req"].(*http.Request) //nolint:forcetypeassert // must exist
 }
 
 func (c TemplateContext) parentContext() context.Context {
-	return c["_ctx"].(context.Context)
+	return c["_ctx"].(context.Context) //nolint:forcetypeassert // must exist
 }
 
 func (c TemplateContext) Deadline() (deadline time.Time, ok bool) {