ctxscope v1.0.0 — log context that rides on a context.Context

Attributes pinned to a context.Context land on every log line emitted under
it. Two tiers: SetGlobal for process facts that never travel, Set for work
facts that cross a hop via ToJSON/FromJSON.

Extracted from github.com/psyb0t/common-go/scope so it can ship on its own
schedule instead of one shared with gorm, echo, NATS and Temporal. The API is
unchanged apart from the package name.

New in this release: NewHandler, a slog.Handler that applies the context's
scope to every record, so plain slog.InfoContext carries the attributes --
including from code that has never heard of this package.

First release of a new module path, so the sequence starts at v1.0.0.