test: add VM-based full-stack bluetooth tests

Add tests that check PipeWire <-> PipeWire bluetooth audio streaming for
A2DP, BAP, HFP.  The tests use Qemu VMs and don't require Bluetooth
support from HW / kernel.

Full VM images are not required; similarly to BlueZ kernel tester these
use (read-only) mount of host filesystem.  A monolithic kernel image
with suitable config is required.  The bluetoothd binary installed on
host is used if found; otherwise tests are skipped.

These test depend on https://github.com/pv/pytest-bluezenv which manages
the VM setup.

To launch:

    python3 -m pip install pytest-bluezenv
    meson devenv -C builddir -w . python3 -m pytest test --kernel-build -v

which also builds a kernel image with required options.

test/bluezenv/conftest.py

@@ -0,0 +1,95 @@
+# -*- coding: utf-8; mode: python; eval: (blacken-mode); -*-
+# SPDX-FileCopyrightText: Copyright © 2026 Pauli Virtanen
+# SPDX-License-Identifier: MIT
+
+import pytest
+import warnings
+
+from pytest_bluezenv import Bluetoothd
+
+
+@pytest.fixture
+def paired_hosts(hosts, host_setup):
+    """
+    Provide two hosts, paired with each other, and the first one Central
+    """
+
+    le = any(
+        "ControllerMode = le" in (p.conf or "")
+        for plugins in host_setup["setup"]
+        for p in plugins
+        if isinstance(p, Bluetoothd)
+    )
+
+    if le:
+        yield from _pair_le(hosts)
+    else:
+        yield from _pair_bredr(hosts)
+
+
+def _pair_bredr(hosts):
+    host0, host1 = hosts
+
+    host0.bluetoothctl.send("scan on\n")
+    host0.bluetoothctl.expect(f"Controller {host0.bdaddr.upper()} Discovering: yes")
+
+    host1.bluetoothctl.send("pairable on\n")
+    host1.bluetoothctl.expect("Changing pairable on succeeded")
+    host1.bluetoothctl.send("discoverable on\n")
+    host1.bluetoothctl.expect(f"Controller {host1.bdaddr.upper()} Discoverable: yes")
+
+    host0.bluetoothctl.expect(f"Device {host1.bdaddr.upper()}")
+    host0.bluetoothctl.send(f"pair {host1.bdaddr}\n")
+
+    idx, m = host0.bluetoothctl.expect(r"Confirm passkey (\d+).*:")
+    key = m[0].decode("utf-8")
+
+    host1.bluetoothctl.expect(f"Confirm passkey {key}")
+
+    host0.bluetoothctl.send("yes\n")
+    host1.bluetoothctl.send("yes\n")
+
+    host0.bluetoothctl.expect("Pairing successful")
+
+    yield hosts
+
+
+def _pair_le(hosts):
+    host0, host1 = hosts
+
+    host0.bluetoothctl.send("scan on\n")
+    host0.bluetoothctl.expect(f"Controller {host0.bdaddr.upper()} Discovering: yes")
+
+    host1.bluetoothctl.send("advertise on\n")
+    host1.bluetoothctl.expect("Advertising object registered")
+
+    host0.bluetoothctl.expect(f"Device {host1.bdaddr.upper()}")
+    host0.bluetoothctl.send(f"pair {host1.bdaddr.upper()}\n")
+
+    # BUG!: if controller is power cycled off/on at boot (before bluetoothd)
+    # BUG!: which is what the tester here does,
+    # BUG!: bluetoothd MGMT command to enable Secure Connections Host Support
+    # BUG!: fails and we are left with legacy passkey. It seems we get randomly
+    # BUG!: one of these depending on what state controller/kernel were before
+    # BUG!: btmgmt power off/on
+
+    idx, m = host0.bluetoothctl.expect(
+        [r"\[agent\].*Passkey:.*m(\d+)", r"Confirm passkey (\d+).*:"]
+    )
+    key = m[0].decode("utf-8")
+
+    if idx == 0:
+        warnings.warn(
+            "BUG: we got passkey authentication, bluetoothd/kernel should be fixed"
+        )
+        host1.bluetoothctl.expect(r"\[agent\] Enter passkey \(number in 0-999999\):")
+        host1.bluetoothctl.send(f"{key}\n")
+    else:
+        host1.bluetoothctl.expect(f"Confirm passkey {key}")
+
+        host0.bluetoothctl.send("yes\n")
+        host1.bluetoothctl.send("yes\n")
+
+    host0.bluetoothctl.expect("Pairing successful")
+
+    yield hosts