feat: add schema_version to JSONL outputs and remove dead code

- Add schema_version (archivebox.VERSION) to all to_jsonl() outputs:
  - Snapshot.to_jsonl()
  - ArchiveResult.to_jsonl()
  - Binary.to_jsonl()
  - Process.to_jsonl()

- Update CLI commands to use model methods directly:
  - archivebox_snapshot.py: snapshot.to_jsonl()
  - archivebox_extract.py: result.to_jsonl()

- Remove dead wrapper functions from misc/jsonl.py:
  - snapshot_to_jsonl()
  - archiveresult_to_jsonl()
  - binary_to_jsonl()
  - process_to_jsonl()
  - machine_to_jsonl()

- Update tests to use model methods directly

archivebox/machine/models.py

@@ -246,8 +246,10 @@ class Binary(ModelWithHealthStats):
         """
         Convert Binary model instance to a JSONL record.
         """
+        from archivebox.config import VERSION
         return {
             'type': 'Binary',
+            'schema_version': VERSION,
             'id': str(self.id),
             'machine_id': str(self.machine_id),
             'name': self.name,
@@ -626,8 +628,10 @@ class Process(ModelWithHealthStats):
         """
         Convert Process model instance to a JSONL record.
         """
+        from archivebox.config import VERSION
         record = {
             'type': 'Process',
+            'schema_version': VERSION,
             'id': str(self.id),
             'machine_id': str(self.machine_id),
             'cmd': self.cmd,