Breaking: GpioChip.close() returns a Future and must be awaited.

A line-info watcher blocks in poll(2) on the chip's own descriptor, so the chip cannot close that descriptor until the watcher has actually left the syscall — descriptor numbers are reused the instant they are free, and a straggling read would land on an unrelated file. LineRequest.close() is already async for exactly this reason; the chip now matches. Add await.

• GpioChip.watchLineInfo(offsets) — a Stream<LineInfoChanged> of requests, releases and reconfigurations, as the kernel reports them, including changes made by other processes. unwatchLineInfo(offset) stops reporting one line; watchedLines says which are being watched.

  lineInfo() gives a snapshot that is stale the moment it returns. Until now a collision with another process surfaced only as EBUSY at request time, too late to do anything but fail.

• LineInfoChanged carries the change kind, the line's state after the change, and the kernel's timestamp. It is deliberately not part of the LineEvent sealed hierarchy: these arrive on a different descriptor and mean something different, and adding a variant to a sealed type would break every exhaustive switch already written against it.

• LineChangeKind.fromValue maps an unrecognised kind to reconfigured rather than throwing, so a future kernel adding a fourth type cannot kill a running program.

• FakeKernel models watches, so consumers can test this without hardware.

The ioctls were already bound in the ABI layer; only the public surface was missing.

• Shortened the package description to the 60-180 characters pub.flutter-io.cn scores. 0.1.0 shipped at ~258 and took 0/10 on "Provide a valid pubspec.yaml" for it; the long-form pitch lives in the README, where it belongs. A published pubspec is immutable, so this needed a release of its own. A test now pins the range.

No API changes.

First release.

• Linux GPIO over /dev/gpiochip* using the v2 userspace ABI, in pure Dart via dart:ffi and libc. No native library, no bundled binaries.
• Chip discovery by label and line lookup by name, so code survives the probe-order renumbering that moves a Pi 5's header between gpiochip0 and gpiochip4.
• Requests of up to 64 lines claimed in one ioctl, read and written atomically. Initial output values are applied by the claiming ioctl, so a line never passes through an undefined state.
• Full per-line configuration: direction, bias, drive, active-low, edge detection, and kernel-side debounce.
• Edge events as a Stream, timestamped by the kernel in the interrupt handler. timestampNs carries the raw nanoseconds; timestamp is a microsecond-resolution Duration convenience.
• LineEventsDropped — when the kernel's event FIFO overflows, the loss is reported rather than silent. The v2 ABI's sequence numbers are what make this possible.
• GpioException maps errno to an actionable message: EACCES gives the udev rule, EBUSY names the consumer holding the line, ENOTTY says the path is not a gpiochip, and EINVAL — which is what a kernel older than 5.10 actually returns for a v2 ioctl — says so.
• package:gpio/gpio_testing.dart — an in-memory kernel for testing GPIO code on machines without GPIO.

Requires Linux 5.10 or newer. There is no v1 fallback, by design.