fix: improve file based execution with namespaced php snippets

[louiswol94]

No description provided.

[louiswol94]

Fixes #275

[sheabunge]

Might be worth adding a specific filter (e.g. code_snippets_php_snippet_file_header) that just includes the code to be prepended, so it can be easily appended to if desired.

[louiswol94]

Might be worth adding a specific filter (e.g. code_snippets_php_snippet_file_header) that just includes the code to be prepended, so it can be easily appended to if desired.

Discussed offline ✅