Upgrading from v0.6.1 can use a rolling update.

- A Durable Object `stub.fetch()` that a peer forwards now rejects when the handler fails on the owner, as it does locally, and the handler does not run again. - A Worker that returns a WebSocket response to a request without `Upgrade: websocket` now fails with a `TypeError` and a 500. - `celld dev` accepts `export NAME=value` lines and multi-line quoted values in `.env` files, and skips an entry that cannot be a binding with a warning. - Epoch GC (`CELLD_LTX_RETENTION_SECS`) also runs on nodes with bucket durability. - LTX capture recovers a torn WAL header when a database opens, so capture no longer skips commits after a crash. - A failed or abandoned eviction no longer stops compaction for the rest of a cell's activation.

Issues fixed:

- #243: `celld dev` reads `.env` and `.env.local` when there is no `.dev.vars`, as `wrangler dev` does. - #245: A fleet with one follower recruits a second one when a peer becomes available. - #246: Follower disk use stays bounded after a snapshot eviction or a deleted facet. - #247: `self` is defined in Worker, Durable Object, and Worker Loader isolates. - #248: `getDurableObjectClass()` accepts a plain class that extends no runtime base. - #252: WebSockets work in Durable Object facets, including outbound sockets that a facet opens. - #255: A deploy no longer deadlocks a Durable Object handler. - #257: A fetch to a loaded Worker honors the caller's `AbortSignal`, including `AbortSignal.timeout()`.