v0.16.2

Fixes for issues found by running a real project's full gate on 0.16.1 (FP-19).

Fixed

• Android failure screenshots were corrupt. The screenshot is saved on the host from the RPC's base64 data, and
  PullArtifacts then re-read that host path through adb exec-out run-as ... cat; cat printed "No such file" on
  stdout (exit 0) and that text overwrote the PNG. A screenshot already on the host is now kept, and anything pulled from
  a device must start with a PNG/JPEG signature or it is reported as an error instead of written as an image.
• Cold-launch race on Android (and iOS simulators): dialing a few seconds after launch could end in
  unexpected EOF and then a 401, because the token readable on the device was still the previous app instance's. When
  the CLI auto-detected the token it now re-reads it on a 401 and retries for up to 12 seconds. An explicit --token
  still fails fast.
• The "agent port is held by" hint now says what holds it: an adb port forward (with adb forward --remove), an iOS
  simulator app (with its simulator UDID and simctl terminate), or any other process. It used to print the same text for
  the first two.

Changed

• A tap that cannot reach its target is no longer silent. When something else is on top at the tap point, the agent
  returns a warning (tap target #id is covered by another widget at (x, y) ..., with the visible texts/keys) and the
  CLI prints it. The tap still happens, as for a real user.
• A tap now waits (up to 1.5 s) while a scrollable around its target is still scrolling: Flutter ignores pointer events
  during scroll activity, so a tap right after scroll ... until ... appears could be dropped. Costs nothing when
  nothing is scrolling.

Not changed

• --grant notifications taps Allow as soon as the iOS notification alert is up, which can be right after a relaunch and
  before the app has visibly asked. That is intended (the alert is what is answered); it is harmless.
• Whether the silent tap after scroll ... until on Android is fully explained by the two changes above could not be
  reproduced without that app; the new warning will name the cause if it happens again.