port-target-cache not available with pytest-xdist (RDT-1277)

[hfudev]

https://github.com/espressif/esp-bsp/actions/runs/14508751792/job/40703558008

[gw10] linux -- Python 3.11.12 /usr/local/bin/python3.11
/usr/local/lib/python3.11/site-packages/pytest_embedded/plugin.py:630: in port_target_cache
    with shelve.open(_cache_file_path) as f:
/usr/local/lib/python3.11/shelve.py:243: in open
    return DbfilenameShelf(filename, flag, protocol, writeback)
/usr/local/lib/python3.11/shelve.py:227: in __init__
    Shelf.__init__(self, dbm.open(filename, flag), protocol, writeback)
/usr/local/lib/python3.11/dbm/__init__.py:95: in open
    return mod.open(file, flag, mode)
E   _gdbm.error: [Errno 11] Resource temporarily unavailable: '/tmp/pytest-embedded/pytest-embedded-cache/port_target_cache'

During handling of the above exception, another exception occurred:
/usr/local/lib/python3.11/site-packages/pytest_embedded/plugin.py:[63](https://github.com/espressif/esp-bsp/actions/runs/14508751792/job/40703558008#step:8:64)3: in port_target_cache
    os.remove(_cache_file_path)
E   FileNotFoundError: [Errno 2] No such file or directory: '/tmp/pytest-embedded/pytest-embedded-cache/port_target_cache'

For now, the port_target_cache is held for the entire process. Let's change it to be read and written on-demand, using a file lock. Since pytest-xdist runs tests with multiprocessing, standard multiprocessing.Lock or threading.Lock won't work.