Commit 04c680a moved the runtime directory into its own package, but the strict server middleware function typedefs really don't need to be in a separate module.

Move these to the codegen, and we can delete them from runtime. We'll embed those typedefs into the generated code.

It looks like this in generated code:

type StrictHandlerFunc = strictecho.StrictEchoHandlerFunc
type StrictMiddlewareFunc = strictecho.StrictEchoMiddlewareFunc

We can simply replace it with inline types.