feat: deltachat_rpc_client.Rpc accepts rpc_server_path for using a particular deltachat-rpc-server (#7493)

also simplifies and make more readable popen-call to rpc-server 

addresses #7428

deltachat-rpc-client/tests/test_rpc_virtual.py

@@ -0,0 +1,20 @@
+import subprocess
+import sys
+from platform import system  # noqa
+
+import pytest
+
+from deltachat_rpc_client import DeltaChat, Rpc
+
+
+@pytest.mark.skipif("system() == 'Windows'")
+def test_install_venv_and_use_other_core(tmp_path):
+    venv = tmp_path.joinpath("venv1")
+    subprocess.check_call([sys.executable, "-m", "venv", venv])
+    python = venv / "bin" / "python"
+    subprocess.check_call([python, "-m", "pip", "install", "deltachat-rpc-server==2.20.0"])
+    rpc = Rpc(accounts_dir=tmp_path.joinpath("accounts"), rpc_server_path=venv.joinpath("bin", "deltachat-rpc-server"))
+
+    with rpc:
+        dc = DeltaChat(rpc)
+        assert dc.rpc.get_system_info()["deltachat_core_version"] == "v2.20.0"