Smoketests: remove interface for using a module source string; always require a precompiled module

Smoketests which use precompiled modules have better performance characteristics than those that use modules with source strings (mostly because our CI can be smarter about them), so we want to require that all smoketests use precompiled modules. Currently, we have a few smoketests which use non-precompiled modules specifically because they assert that the compilation will fail. We should rewrite those tests so that they either call spacetime build explicitly or use a separate, purpose-built abstraction, rather than calling a normal Smoketest constructor and asserting that it fails. Then, we should remove the Smoketest constructor that accepts a source string, so that all smoketests have to use precompiled modules.

Comienza localizando el constructor de Smoketest que acepta una cadena de origen y todos los smoketests que lo utilizan. Revisa los casos existentes de fallos de compilación y confirma después que utilizan una compilación explícita o una abstracción separada, y que todos los Smoketest restantes utilizan un módulo precompilado; el constructor ya no debería aceptar cadenas de origen.