hashing

Content identity: what a tree is, independent of where it sits.

• [.content_hash][] — ContentHash (what names an object) and CallKey (what names a memoized call).
• [.merkle][] — a tree hashes as the merkle of its entries: hash_tree, hash_bytes, call_key, and the per-kind hashing domains.
• [.stat_cache][] — Stat, the identity of a file without reading it, and the HashCache that remembers a hash for as long as the stat holds.

This __init__ is documentation-only; internal modules import from the leaf modules directly.