Proposal targets net/http's pre-io/fs file server API

A proposal to deprecate net/http's Dir, FileServer, FileSystem, FS, and NewFileTransport lands on the tracker, arguing the interface predates io/fs.FS and should give way to it. It pairs nicely with the latest Fallthrough episode, which digs into Austin's plan for taming the proposal backlog itself, so the meta-question of how Go handles proposals is getting aired at the same time as a concrete one. Elsewhere, a write-up on singleflight covers what duplicate suppression does not solve once you factor in cancellation and shutdown, which is the kind of detail that tends to bite in production.