`path` type path params can have default or be optional
According to [document](https://hapticx.github.io/happyx/happyx#path-params-%F0%9F%9B%A0-validation-%E2%9A%99)
> `path`: like string but includes / chars. Doesn't provides optional and default.

But in fact, HappyX can handle it without problem (checked with `-d:spaDebug`), with one exception `$p:path=/`, this generates incorrect regex (`re2("^/photo-rename([\\S]+)=/$")`), but `{p:path=/}` work as expect.

Currently, if there is a problem with the processing of path parameters, you can only use `-d:spaDebug` or `-d:ssrDebug` to view the generated code to confirm that it matches your expectations. Would it be appropriate to change this to a compile-time error?