base-item: Use the new GeglBuffer codec API

Unlike the older GeglOperation based API, the newer API is cancellable,
supports error handling, and doesn't make any assumptions about the
paths being UTF-8 encoded.

#63
3 jobs for wip/rishi/buffer-decoder in 9 minutes and 24 seconds (queued for 1 second)
Status Job ID Name Coverage
  Test
failed #229674
flatpak

00:09:24

 
  Review
skipped #229675
review
skipped #229676
allowed to fail manual
stop_review
 
Name Stage Failure
failed
flatpak Test
**
gnome-photos:ERROR:../tests/unit/photos-test-gegl-buffer.c:2492:photos_test_gegl_buffer_check_new_from_stream_at_scale: assertion failed (checksum_decoded == checksum): ("8cbfe687e8793caa3bd7bf689234acb465b16b73ab7585bf0d3377ad9750c95c" == "dd4e5b1965ce58bd017557014f06c120051454afba9b5f983153175c9666b2e9")
-------

Full log written to /builds/GNOME/gnome-photos/_build/meson-logs/testlog.txt
FAILED: meson-test
/usr/bin/meson test --no-rebuild --print-errorlogs
ninja: build stopped: subcommand failed.
ERROR: Job failed: exit code 1