rebuild_rec followed parent/child links with no depth limit, so a channel
graph in which a channel is its own ancestor recursed until the process ran
out of memory.
Cap the depth and give the whole rebuild a single node budget. Accumulating
into one slice rather than returning a new slice per node makes that budget
apply to the tree as a whole instead of to each level, and removes an
allocation per node.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Storm Dragon