Vendor the XML inside the package so it ships in the wheel

uv_build packages only src/mcbebop, so arsdk-xml/ at the repo root was
absent from the wheel and every install would have failed to find the
command definitions. Caught during the protocol build.

tests/test_packaging.py

@@ -30,7 +30,7 @@ def test_server_builds():
 def test_vendored_xml_present_and_parses():
     import xml.etree.ElementTree as ET
 
-    root = Path(__file__).parent.parent / "arsdk-xml"
+    root = Path(__file__).parent.parent / "src" / "mcbebop" / "arsdk-xml"
     total = 0
     for name in ("common.xml", "ardrone3.xml"):
         proj = ET.parse(root / name).getroot()