S3 binary caches now use virtual-hosted-style URLs by default for
standard AWS endpoints. Path-style endpoints (s3.region.amazonaws.com)
only serve HTTP/1.1, preventing HTTP/2 multiplexing and causing TCP
TIME_WAIT socket exhaustion under high concurrency. Virtual-hosted-style
endpoints (bucket.s3.region.amazonaws.com) support HTTP/2, enabling
multiplexing with the existing CURLPIPE_MULTIPLEX configuration.
Add a new `addressing-style` store option (auto/path/virtual) to control
this behavior. `auto` (default) uses virtual-hosted-style for standard
AWS endpoints and path-style for custom endpoints. `path` forces
path-style for backwards compatibility. `virtual` forces virtual-hosted-
style for all endpoints including custom ones.
Fixes: https://github.com/NixOS/nix/issues/15208
759f6c856b