Reader

A pull-based source of elements. Returns elements until closed.

==Thread safety== Reader instances are ''not'' thread-safe. They are designed for single-threaded, pull-based consumption. Do not share a Reader across threads without external synchronization.

==Termination== The read method returns elements while available, or a caller-chosen sentinel when closed. For errors, read throws — either the raw exception, or a StreamError wrapping non-Throwable error values. See zio.blocks.streams.internal.StreamError.

==Sentinel-return protocol== Specialized methods (readInt, readLong, etc.) widen the return type and use a caller-chosen sentinel for end-of-stream. These are the hot-path zero-boxing pull methods.

'''Sentinel choice:''' The Int lane uses Long.MinValue (safe because no Int value widens to Long.MinValue). Long and Double paths that must distinguish end-of-stream use the identity-only EndOfStream marker so every value remains representable. The Float lane uses Double.MaxValue (safe because Float.MaxValue widened to Double is distinct from Double.MaxValue).

==Laws==

• isClosed is monotone: once true it never returns false.
• When isClosed and buffer is empty: read(sentinel) returns the sentinel.