[ENH] Enable search sorting by mostdownload

[mathdugre]

Closes #1239

[mathdugre]

This is my initial attempt at adding the functionality to search by "most download".

Unfortunately, I could not run the dev environment to test, as I ran into this error:

invenio-cli check-requirements --development             (enh/enable-mostdl-search)zenodo-rdm

Checking pre-requirements...
Checking Python version...
Python version OK. Got 3.13.6.
Checking Pipenv is installed...
Traceback (most recent call last):
  File "/Users/mathdugre/.local/share/uv/tools/invenio-cli/lib/python3.13/site-packages/invenio_cli/commands/requirements.py", line 175, in check_pipenv_installed
    result = run_cmd(["pipenv", "--version"])
  File "/Users/mathdugre/.local/share/uv/tools/invenio-cli/lib/python3.13/site-packages/invenio_cli/helpers/process.py", line 35, in run_cmd
    p = popen(command, stdout=PIPE, stderr=PIPE)
  File "/Users/mathdugre/.local/share/uv/python/cpython-3.13.6-macos-aarch64-none/lib/python3.13/subprocess.py", line 1039, in __init__
    self._execute_child(args, executable, preexec_fn, close_fds,
    ~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
                        pass_fds, cwd, env,
                        ^^^^^^^^^^^^^^^^^^^
    ...<5 lines>...
                        gid, gids, uid, umask,
                        ^^^^^^^^^^^^^^^^^^^^^^
                        start_new_session, process_group)
                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/mathdugre/.local/share/uv/python/cpython-3.13.6-macos-aarch64-none/lib/python3.13/subprocess.py", line 1972, in _execute_child
    raise child_exception_type(errno_num, err_msg, err_filename)
FileNotFoundError: [Errno 2] No such file or directory: 'pipenv'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/Users/mathdugre/.local/bin/invenio-cli", line 10, in <module>
    sys.exit(invenio_cli())
             ~~~~~~~~~~~^^
  File "/Users/mathdugre/.local/share/uv/tools/invenio-cli/lib/python3.13/site-packages/click/core.py", line 1485, in __call__
    return self.main(*args, **kwargs)
           ~~~~~~~~~^^^^^^^^^^^^^^^^^
  File "/Users/mathdugre/.local/share/uv/tools/invenio-cli/lib/python3.13/site-packages/click/core.py", line 1406, in main
    rv = self.invoke(ctx)
  File "/Users/mathdugre/.local/share/uv/tools/invenio-cli/lib/python3.13/site-packages/click/core.py", line 1873, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
                           ~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^
  File "/Users/mathdugre/.local/share/uv/tools/invenio-cli/lib/python3.13/site-packages/click/core.py", line 1269, in invoke
    return ctx.invoke(self.callback, **ctx.params)
           ~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/mathdugre/.local/share/uv/tools/invenio-cli/lib/python3.13/site-packages/click/core.py", line 824, in invoke
    return callback(*args, **kwargs)
  File "/Users/mathdugre/.local/share/uv/tools/invenio-cli/lib/python3.13/site-packages/invenio_cli/cli/cli.py", line 72, in check_requirements
    run_steps(steps, on_fail, on_success)
    ~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/mathdugre/.local/share/uv/tools/invenio-cli/lib/python3.13/site-packages/invenio_cli/cli/utils.py", line 21, in run_steps
    response = step.execute()
  File "/Users/mathdugre/.local/share/uv/tools/invenio-cli/lib/python3.13/site-packages/invenio_cli/commands/steps.py", line 41, in execute
    response = self.func(**self.args)
  File "/Users/mathdugre/.local/share/uv/tools/invenio-cli/lib/python3.13/site-packages/invenio_cli/commands/requirements.py", line 191, in check_pipenv_installed
    error=f"Pipenv not found. Got {result.error}.", status_code=1
                                   ^^^^^^
UnboundLocalError: cannot access local variable 'result' where it is not associated with a value