docs: add missing safety sections for public unsafe APIs

[mevinagrise]

This PR adds missing # Safety sections to the public unsafe APIs exposed by the crate.

Specific changes include:

• Added a # Safety section to LinkedList::push.
• Added a # Safety section to Heap::add_to_heap.
• Added a # Safety section to Heap::init.
• Added a # Safety section to Heap::dealloc.

Why this is useful:

• These functions are public and unsafe, so their caller obligations should be stated explicitly.
• This improves the generated documentation for downstream users.
• It also resolves the clippy::missing_safety_doc findings for these APIs.

Testing:

• Ran cargo test.
• Ran cargo clippy --all-targets --all-features -- -D warnings.

Note:
After this change, the missing_safety_doc findings are resolved. The remaining Clippy failure is clippy::result_unit_err in Heap::alloc, which involves a public API change and is intentionally left for a separate discussion.

[Copilot]

Pull request overview

This PR improves the crate’s public API documentation by adding missing Rustdoc # Safety sections to public unsafe functions, addressing clippy::missing_safety_doc for those APIs.

Changes:

• Documented caller safety requirements for LinkedList::push.
• Documented caller safety requirements for Heap::{add_to_heap, init, dealloc}.
• Minor Rustdoc formatting/punctuation improvements around those APIs.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 4 comments.

File	Description
src/linked_list.rs	Adds a # Safety section to the intrusive list push operation to clarify caller obligations.
src/lib.rs	Adds # Safety sections to heap initialization/growth and deallocation entry points to improve unsafe API docs.

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[mevinagrise]

Updated to make this safety requirement explicit.