Add [[nodiscard]] to VkShaderModule::loadFromFile, Shader::loadFromFile/
loadFromSource, AssetManifest::load, DbcLoader::load — all return bool
indicating success/failure that callers should check.
Suppress with (void) at 17 call sites where validity is checked via
isValid() after loading rather than the return value (m2_renderer
recreatePipelines, swim_effects recreatePipelines).