fix: stack overflow on pre-existing Symbol circular references (#1106)

[dyk1454683243-sudo]

Fixes #1106.

Problem

Starting in 10.0.4, Immer walks symbol keys. Objects that use symbols for child-to-parent links (skipped by JSON.stringify / Immer 9) then hit Maximum call stack size exceeded.

On current main, produce() itself is already safe: handleValue tracks visited objects. current() was not. It:

1. Recursed into nested non-drafts with no cycle guard.
2. Always used strict iteration for those nodes (strict was not passed down), so symbol links were followed even when setUseStrictIteration(false) (the default).

That is the remaining overflow for the issue’s data shape — e.g. produce(parent, d => { d.name = "x"; current(d) }).

Change

In current():

• Remember objects already snapshotted (WeakMap) so circular refs (including symbol keys) reuse the snapshot instead of recursing forever.
• Pass the same iteration mode into nested non-drafts.

No other finalization / copy behavior is changed.

Tests

__tests__/symbol-circular.js covers the issue’s cases:

• produce on parent, nested child, and child-as-root
• reading a pre-existing symbol without leaking drafts
• current() after parent/child updates
• self-referential symbol props
• setUseStrictIteration(true) and strict shallow copy
• symbols assigned inside a recipe (still no leaked drafts; produce leaks proxy objects when symbols are present #1087)

Notes

Circular references added inside a recipe were already fine; this is only about pre-existing symbol cycles. Plain (enumerable) circular refs remain unsupported, as documented.