Fix infinite forEachChild loop on some nodes in JS API

[auvred]

If we cache by text position rather than by node index, traversing namespace foo.bar {} ends up in an infinite loop.

Note: #2835 supersedes this PR. If the team plans to adopt the approach of #2835, this PR can be closed.

[Copilot]

Pull request overview

Fixes an infinite forEachChild traversal loop in the JS API AST materialization by changing the child-cache keying strategy to use node indices (stable/unique) instead of text positions (can collide on some syntactic forms like namespace foo.bar {}).

Changes:

• Cache RemoteNode / RemoteNodeList children by node index rather than by pos in _packages/api/src/node.ts.
• Add a sync API regression test that traverses namespace foo.bar {} and fails fast if traversal loops.

Reviewed changes

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

File	Description
_packages/api/src/node.ts	Switch _children cache key from text position to node index to prevent cache collisions and traversal cycles.
_packages/api/test/api.sync.test.ts	Add regression test ensuring forEachChild traversal terminates correctly on dotted namespaces.