stream: use busy metadata

When we get a buffer from the server, mark it busy, when we queue it
again, mark it unbusy.
Refuse to dequeue a buffer when it is busy.
2 jobs for busy-meta in 59 seconds
latest
Status Job ID Name Coverage
  Container
passed #1790339
build-container

00:00:24

 
  Build
failed #1790340
build

00:00:35

 
Name Stage Failure
failed
build Build
'SPA_META_LAST == 7' failed at ../spa/tests/test-buffer.c:57 test_abi()
-------

Full log written to /builds/pipewire/pipewire/build/meson-logs/testlog.txt
FAILED: meson-test
/usr/bin/meson test --no-rebuild --print-errorlogs
ninja: build stopped: subcommand failed.
make: *** [Makefile:27: test] Error 1
ERROR: Job failed: exit code 1