Add BeginTx(ctx, pgx.TxOptions) to Client interface for explicit isolation level and
read-only transaction control; Begin refactored as a convenience wrapper calling
BeginTx(ctx, pgx.TxOptions{}). Add Stats() *pgxpool.Stat to Component interface for
connection pool observability. Bump all micro-lib dependencies (logz, health, launcher,
xerrors) from v0.9.0 to v1.0.0. API committed as stable.