Don't over-allocate for request bodies

…ancel

Handle hyper providing us incomplete requests

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

After a full docker restart, a replacement ingester can bind its unix
socket while the old container is still draining; the old server's
stop() then unlinked the path by name, deleting the new server's socket.
The new server keeps listening on an unlinked inode and never recovers
(BetterStackHQ Linear T-8292).

- start() now binds to a unique temp path and atomically renames it over
  the target, so the path always points at a live socket and takeover of
  a still-bound path is a single step.
- stop() records the bound socket file's (dev, ino) and only unlinks the
  path if it still matches, so an older generation never removes a newer
  generation's socket.

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>