fix: render error types as strings in human log sink (#224)

`formatValue` checked `reflect.Struct` before checking the `error`
interface, so struct-typed errors like `context.DeadlineExceeded`
were serialized via `json.Marshal` as `{}` instead of their error
string.

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

chore: update to v3 (#223)

fix!: don't panic, only accept typed log Fields (#222)

* fix: don't panic, only accept typed log Fields

* slogtest errors if we fail to stringify a field value

chore: update all deps (#182)

chore: migrate to go.opentelemetry.io tracing (#181)

Support keysAndArgs API of stdlib slog (#173)

Pretty-print driver.Valuer

Fix test logger

Don't panic on nil values

Switch human logger from JSON to logfmt (#170)