v1.0.0

The API is now stable. Everything a caller can reach is declared in this
module's own packages and documented on pkg.go.dev, and from here on a change
that breaks a compiling program needs a /v2 import path rather than a
version bump. Additions stay additions. The measurement algorithm, the wire
behaviour and schema_version are unchanged from 0.5.0: this release is about
what the API promises, not what the test does.

Upgrading from 0.5.0 touches three things, all of them mechanical, and the
compiler finds every one.

Changed

• The public API no longer aliases internal types. LatencyStats,
  StageMedians, Confidence and StabilityParams were aliases of
  internal/engine types, so pkg.go.dev showed callers a bare
  type StabilityParams = engine.StabilityParams and none of the fields, and a
  rename inside the engine broke importers with nothing to warn us. They are
  declared in the library package now, with the documentation the aliases hid.
  Field names, types and JSON tags are unchanged, so existing code compiles and
  schema_version stays 1; only code that named engine.* types through an
  alias is affected.
• Run is the only entry point. RunWithEvents is gone; its sink is
  Options.Events, which carries the same concurrency contract (RES-8).
  Replace RunWithEvents(ctx, t, o, sink) with Run(ctx, t, o) after setting
  o.Events = sink.
• ParseServerConfig, DefaultStabilityParams and LatencySample are no
  longer exported. Discovery happens inside Run, a zero StabilityParams
  already selects the defaults, and no Result field ever reached a
  LatencySample. ErrInvalidConfig stays exported for errors.Is.

Added

• scripts/api-compat.sh and a CI job report incompatible public API changes
  since the newest release tag. The job is advisory in this release and becomes
  blocking immediately after it, once there is a v1 tag to compare against.