builtins.deepSeq on deeply nested structures (e.g., a linked list with
100,000 elements) caused an uncontrolled OS-level stack overflow with
no Nix stack trace.
Fix by adding call depth tracking to forceValueDeep, integrating with
Nix's existing max-call-depth mechanism. Now produces a controlled
"stack overflow; max-call-depth exceeded" error with a proper stack
trace.
Closes: https://github.com/NixOS/nix/issues/7816
