lib: simplify debug_map_push
lib: simplify naming in debug_map_push
lib/tree: introduce tree locking
lib/tree: fix lock conflict due to tree_insert -> tree_search
doc: add TODO related to merge/split hysteresis
lib/tree: return index instead of pointer in node_search
lib/tree: make node_split param names consistent
lib/tree: use node addrs in node_{used,free}
lib/tree: add uninitialized pointer protections in node_merge
lib/tree: eliminate {leaf,branch}_xfer_half
lib/tree: simplify branch_zero
lib/tree: simplify leaf_zero
lib/tree: add {leaf,branch}_shift_{forward,backward}
lib/tree: fix bug in leaf_zero
lib/tree: add branch_insert_naive
lib/tree: add {leaf,branch}_xfer