[tomas-zijdemans]

Adds IntrusiveList and IntrusiveListNode at
@std/data-structures/unstable-intrusive-list. The list stores its links on
the caller's objects, so whoever holds a node can remove it or move it to the
back in O(1).

Immediate std consumers::

• @std/rate-limit (feat(rate-limit/unstable): add rate limiting module #7237) (waiters)
• @std/cache (feat(cache/unstable): add Cache #7236) (recency order)
• Channel (waiters). Can adopt IntrusiveList once it's stable.

Later, maybe: Semaphore in @std/async/unstable-semaphore keeps its own waiter queue. If acquire() gets a signal option, a cancelled waiter has to leave the middle of that queue, which is what this list does in O(1).

An intrusive list keeps its prev and next links on the elements themselves,
not in wrapper nodes the list allocates. Code that holds an element can unlink
it in O(1) without a search, and the list allocates nothing per element. It's the
usual structure for wait queues and LRU orders:

• Linux list.h,
• Rust's intrusive-collections,
• Tokio's waiter lists
• .NET's LinkedList<T>

JavaScript has no built-in one (Node has internal/linkedlist.js which Deno ports). Libraries that need it write their own. Cache did.

Nodes extend IntrusiveListNode, which keeps the links and the owning list in
private fields. Every method that takes a node throws a TypeError for a
node from another list, and removing a detached node returns false. There's no clear(),
because every consumer visits each node when it empties its list, and an O(1)
reset would leave nodes claiming a list they left.

I used Claude Code to help investigate and write this change.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.05%. Comparing base (f834d02) to head (09b2790).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7346      +/-   ##
==========================================
+ Coverage   95.04%   95.05%   +0.01%     
==========================================
  Files         619      619              
  Lines       52012    51898     -114     
  Branches     9450     9425      -25     
==========================================
- Hits        49434    49333     -101     
+ Misses       2031     2022       -9     
+ Partials      547      543       -4     

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.