meson: copy .py files to build directory

This seems to do the trick:
$ ninja -C build
$ PYTHONPATH=build/src/ python -c 'from systemd import id128; print(id128)'
<module 'systemd.id128' from '/home/zbyszek/src/python-systemd/build/src/systemd/id128.cpython-313-x86_64-linux-gnu.so'>
$ PYTHONPATH=build/src/ pytest build/src/systemd/test
...
============================ test session starts =============================
platform linux -- Python 3.13.4, pytest-8.3.4, pluggy-1.5.0
rootdir: /home/zbyszek/src/python-systemd
configfile: pyproject.toml
plugins: ...
collected 61 items

build/src/systemd/test/test_daemon.py ........................         [ 39%]
build/src/systemd/test/test_id128.py ....                              [ 45%]
build/src/systemd/test/test_journal.py ............................    [ 91%]
build/src/systemd/test/test_login.py .....                             [100%]

============================= 61 passed in 0.21s =============================

Author: keszybz

meson.build

@@ -13,6 +13,8 @@ project(
 python = import('python').find_installation('python3', pure: false)
 python_dep = python.dependency()
 
+fs = import('fs')
+
 libsystemd_dep = dependency('libsystemd')
 
 add_project_arguments(

src/systemd/meson.build

@@ -46,22 +46,18 @@ python.extension_module(
 )
 
 # Install Python modules
-python.install_sources(
+py_files = files(
         '__init__.py',
         'journal.py',
         'daemon.py',
-        subdir: 'systemd',
-)
+)        
 
-# Install test modules
-python.install_sources(
-        'test/test_daemon.py',
-        'test/test_journal.py',
-        'test/test_login.py',
-        'test/test_id128.py',
-        subdir: 'systemd/test',
-)
+python.install_sources(py_files, subdir: 'systemd')
+foreach file: py_files
+        fs.copyfile(file)
+endforeach
 
+# The 'update-constants' target
 include_dir = libsystemd_dep.get_variable(pkgconfig: 'includedir')
 
 update_constants = custom_target(
@@ -73,3 +69,5 @@ update_constants = custom_target(
                 meson.current_source_dir() / 'id128-defines.h',
                 include_dir / 'systemd/sd-messages.h',
         ])
+
+subdir('test')

src/systemd/test/meson.build

@@ -0,0 +1,14 @@
+# SPDX-License-Identifier: LGPL-2.1-or-later
+
+# Install test modules
+py_files = files(
+        'test_daemon.py',
+        'test_journal.py',
+        'test_login.py',
+        'test_id128.py',
+)
+
+python.install_sources(py_files, subdir: 'systemd/test')
+foreach file: py_files
+        fs.copyfile(file)
+endforeach