feat(lint): Add missing_no_std_attribute

[bushrat011899]

Objective

• Contributes to Lint crates that can be #![no_std] but aren't #1569

Details

This lint checks if a crate does not contain the #![no_std] attribute (either bare or through cfg_attr) and suggests adding both it and extern crate std;.

+ #![no_std]
+ extern crate std;

This suggestion is inserted at the ModSpans::inject_use_span point.

Notes

• No AI tooling of any kind was used during the creation of this PR.
• This suggestion can fail if the crate currently relies on items through and exclusive to the std::prelude. I have marked it as Applicability::MaybeIncorrect to reflect this.

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changelog: [missing_no_std_attribute]: add new lint for lack of #![no_std] attribute

[rustbot]

r? @Jarcho

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Why was this reviewer chosen?

The reviewer was selected based on:

• Owners of files modified in this PR: 7 candidates
• 7 candidates expanded to 7 candidates
• Random selection from Jarcho, dswij, llogiq, samueltardieu

[github-actions]

Lintcheck changes for 61ef36d

Lint	Added	Removed	Changed
clippy::missing_no_std_attribute	142	0	0

This comment will be updated if you push new changes

[bushrat011899]

@rustbot author

Looks like the cfg_attr check didn't work as I expected. Will fix that up...

[rustbot]

Reminder, once the PR becomes ready for a review, use @rustbot ready.