Tests: fix unittest build and include BMemoryRingIO shared tests

When change 2966 was merged as hrev56269, it was decided to first introduce
this in libshared instead of libbe.so. The test was moved accordingly, but
not all the code in the unittests was properly updated. This change completes
it.

Note that the test currently crashes, so it needs more investigation whether
that is a test issue or a BMemoryRingIO issue. Fixing this is beyond the
scope of this change.

Change-Id: I0f61d1dd013da904b3e4545db11fefa9da2da0a2
Reviewed-on: https://review.haiku-os.org/c/haiku/+/5676
Tested-by: Commit checker robot <no-reply+buildbot@haiku-os.org>
Reviewed-by: Jérôme Duval <jerome.duval@gmail.com>

Shared Kit: Introduce BMemoryRingIO, a thread-safe ring buffer

This commit introduces a simple thread-safe ring buffer implementation
based on top of BDataIO. The main use case for this class will be to
implement shared buffers between threads for the upcoming refactoring
of Services Kit.

Change-Id: I526bc044b28c91496ad996fabebe538e75647f2c
Reviewed-on: https://review.haiku-os.org/c/haiku/+/2966
Reviewed-by: Jacob Secunda <secundaja@gmail.com>
Reviewed-by: waddlesplash <waddlesplash@gmail.com>
Reviewed-by: Adrien Destugues <pulkomandy@pulkomandy.tk>
Tested-by: Commit checker robot <no-reply+buildbot@haiku-os.org>