chore(license): add SPDX identifiers to all source files

PyreWire is dual-licensed (Apache-2.0 OR GPL-3.0-or-later) and declares
this at the package level in pyproject.toml, but no source file carried a
per-file SPDX tag. Add

    # SPDX-License-Identifier: Apache-2.0 OR GPL-3.0-or-later

to every .py file under src/, tests/, examples/, scripts/ and setup.py
(after the shebang where present), making the license machine-discoverable
for REUSE/SPDX tooling and downstream redistribution.

Add tests/test_spdx_headers.py as a contract test that fails the build if
any source file is missing the tag or declares a different expression, so
the headers cannot silently drift.

Author: justinjoy

examples/01_simple.py

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: Apache-2.0 OR GPL-3.0-or-later
 """Port of wirelog `examples/01-simple` to PyreWire.
 
 Inline EDB facts + a single recursive rule. Uses

examples/02_reachability.py

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: Apache-2.0 OR GPL-3.0-or-later
 """Port of wirelog `examples/02-graph-reachability` to PyreWire.
 
 Transitive closure over a directed graph encoded as inline `edge`

examples/03_bitwise.py

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: Apache-2.0 OR GPL-3.0-or-later
 """Port of wirelog `examples/03-bitwise-operations` to PyreWire.
 
 Demonstrates wirelog's built-in bitwise functors: `band` / `bor` /

examples/04_hash_functions.py

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: Apache-2.0 OR GPL-3.0-or-later
 """Port of wirelog `examples/04-hash-functions` to PyreWire.
 
 Demonstrates wirelog's built-in `hash()` functor for the three tasks

examples/05_crc32_checksum.py

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: Apache-2.0 OR GPL-3.0-or-later
 """Port of wirelog `examples/05-crc32-checksum` to PyreWire.
 
 Demonstrates wirelog's `crc32_ethernet()` built-in by validating frame

examples/06_timestamp_lww.py

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: Apache-2.0 OR GPL-3.0-or-later
 """Port of wirelog `examples/06-timestamp-lww` to PyreWire.
 
 Last-Writer-Wins via the `max()` aggregate: for each key, keep the

examples/07_multi_source_analysis.py

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: Apache-2.0 OR GPL-3.0-or-later
 """Port of wirelog `examples/07-multi-source-analysis` to PyreWire.
 
 Two CRM sources (`src_a`, `src_b`) supply customer records. The

examples/08_delta_queries.py

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: Apache-2.0 OR GPL-3.0-or-later
 """Port of wirelog `examples/08-delta-queries` to PyreWire.
 
 Demonstrates wirelog's delta-callback pipeline through `EasySession.step`.

examples/10_recursive_under_update.py

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: Apache-2.0 OR GPL-3.0-or-later
 """Port of wirelog `examples/10-recursive-under-update` to PyreWire.
 
 Demonstrates that wirelog correctly maintains a RECURSIVE rule under

examples/11_time_evolution.py

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: Apache-2.0 OR GPL-3.0-or-later
 """Port of wirelog `examples/11-time-evolution` to PyreWire.
 
 Each `EasySession.step()` is a discrete time epoch — the delta