Allow for fields w/ epics_signal_rw_rbv, also support long strings/waveforms with PVA backend.

[jwlodek]

Resolves #678

[jwlodek]

(venv) [jwlodek@xf31id1-lab3-ioc1 profile_tst]$ pip freeze | grep aioca
(venv) [jwlodek@xf31id1-lab3-ioc1 profile_tst]$ ./start-bsui.sh 
Python 3.11.10 (main, Sep 24 2024, 09:33:51) [GCC 8.5.0 20210514 (Red Hat 8.5.0-22)]
Type 'copyright', 'credits' or 'license' for more information
IPython 8.29.0 -- An enhanced Interactive Python. Type '?' for help.

IPython profile: tst
DEBUG:setuptools_dso.runtime:Extend DSO search path to '/nsls2/users/jwlodek/.ipython/profile_tst/venv/lib64/python3.11/site-packages/epicscorelibs/lib'
DEBUG:setuptools_dso.runtime:Extend DSO search path to '/nsls2/users/jwlodek/.ipython/profile_tst/venv/lib64/python3.11/site-packages/pvxslibs/lib'
Connecting to manta device 1
DEBUG:ophyd_async.devices:Connecting to pva://XF:31ID1-ES{GigE-Cam:1}cam1:ConvertPixelFormat_RBV
DEBUG:ophyd_async.devices:Connecting to pva://XF:31ID1-ES{GigE-Cam:1}cam1:TriggerSource_RBV
DEBUG:ophyd_async.devices:Connecting to pva://XF:31ID1-ES{GigE-Cam:1}cam1:TriggerMode_RBV
DEBUG:ophyd_async.devices:Connecting to pva://XF:31ID1-ES{GigE-Cam:1}cam1:TriggerOverlap_RBV
....

DEBUG:asyncio:Using selector: EpollSelector
In [1]: await manta1.hdf.file_path.get_value()
DEBUG:asyncio:Using selector: EpollSelector
DEBUG:p4p.client.asyncio:get XF:31ID1-ES{GigE-Cam:1}HDF1:FilePath_RBV request=field(value)
DEBUG:p4p.client.raw:Handler (3, , Value(id:epics:nt/NTScalarArray:1.0, array([ 47, 116, 109, 112,  47, 116, 101, 115, 116,  47,   0], dtype=int8))) -> functools.partial(<bound method BaseEventLoop.call_soon_threadsafe of <_UnixSelectorEventLoop running=True closed=False debug=False>>, <function Context._get_one.<locals>.cb at 0x7f0a1961ef20>)
DEBUG:ophyd_async.devices:get_value() on source pva://XF:31ID1-ES{GigE-Cam:1}HDF1:FilePath_RBV returned /tmp/test/
Out[1]: '/tmp/test/'

DEBUG:asyncio:Using selector: EpollSelector
In [2]: await manta1.hdf.file_path.set("/hello/world")
DEBUG:ophyd_async.devices:Putting value /hello/world to backend at source pva://XF:31ID1-ES{GigE-Cam:1}HDF1:FilePath
DEBUG:p4p.client.asyncio:put XF:31ID1-ES{GigE-Cam:1}HDF1:FilePath <- {'value': [47, 104, 101, 108, 108, 111, 47, 119, 111, 114, 108, 100, 0]} request=field()record[block=true,process=passive]
DEBUG:p4p.client.raw:Handler (3, , None) -> functools.partial(<bound method BaseEventLoop.call_soon_threadsafe of <_UnixSelectorEventLoop running=True closed=False debug=False>>, <function Context._put_one.<locals>.cb at 0x7f0a1b0af240>)
DEBUG:p4p.client.asyncio:put done XF:31ID1-ES{GigE-Cam:1}HDF1:FilePath None
DEBUG:ophyd_async.devices:Successfully put value /hello/world to backend at source pva://XF:31ID1-ES{GigE-Cam:1}HDF1:FilePath

DEBUG:asyncio:Using selector: EpollSelector
In [3]: