Merge bitcoin/bitcoin#33420: test: Avoid interface_ipc.py Duplicate ID errors

e9c52272eb test: Avoid interface_ipc.py Duplicate ID errors (Ryan Ofsky)

Pull request description:

  This change should fix issue https://github.com/bitcoin/bitcoin/issues/33417 reported by zaidmstrr. It's possible to reproduce the `mp/proxy.capnp:0: failed: Duplicate ID @0xcc316e3f71a040fb` error by installing libmultiprocess system-wide, or to one of the locations listed in the python test's `imports` list before the local libmultiprocess subtree, and then running the test.

ACKs for top commit:
  zaidmstrr:
    Tested ACK [e9c5227](e9c52272eb)

Tree-SHA512: 5df7fe767989b91245ce96f7c43b6767b7af49ec6c7007175e462341ffd69e161f21632697804060ce286b3e102a8d141a57a53f7e0e32299ef9a3a69ca8794a

test/functional/interface_ipc.py

@@ -35,7 +35,12 @@ class IPCInterfaceTest(BitcoinTestFramework):
             capnp_dir = Path(capnp.__path__[0]).parent
         src_dir = Path(self.config['environment']['SRCDIR']) / "src"
         mp_dir = src_dir / "ipc" / "libmultiprocess" / "include"
-        imports = [str(capnp_dir), str(src_dir), str(mp_dir)]
+        # List of import directories. Note: it is important for mp_dir to be
+        # listed first, in case there are other libmultiprocess installations on
+        # the system, to ensure that `import "/mp/proxy.capnp"` lines load the
+        # same file as capnp.load() loads directly below, and there are not
+        # "failed: Duplicate ID @0xcc316e3f71a040fb" errors.
+        imports = [str(mp_dir), str(capnp_dir), str(src_dir)]
         return {
             "proxy": capnp.load(str(mp_dir / "mp" / "proxy.capnp"), imports=imports),
             "init": capnp.load(str(src_dir / "ipc" / "capnp" / "init.capnp"), imports=imports),