Limit inner doc comment attributes to Module

[eureka-cpu]

Description

Ran on test branch & working as intended. Only beginning of file //! is collected as DocComment with DocStyle::Inner which is only parsed at the beginning of the Module parsing stage. This ensures that any //! found after the module docs will be treated as normal comments for now. Ref #4112 for tracking further progress in allowing inner doc comments for Item.

Checklist

• I have linked to any relevant issues. Closes Limit inner doc comment attributes to Module #4097
• I have commented my code, particularly in hard-to-understand areas.
• I have updated the documentation where relevant (API docs, the reference, and the Sway book).
• I have added tests that prove my fix is effective or that my feature works.
• I have added (or requested a maintainer to add) the necessary Breaking* or New Feature labels where relevant.
• I have done my best to ensure that my PR adheres to the Fuel Labs Code Review Standards.
• I have requested a review from the relevant team or maintainers.

[mitchmindtree]

Yeah nice, I think this conservative approach and enforcing some consistency like this is the right one 👍 We can reconsider enabling for all items if someone comes across an actual good use-case to have them anywhere else.