Implement Phase 1 tasks 1.5-1.7 + 1.9 (Codec 8/8E/16 parsers + fixture suite)

- Codec 8 parser (1-byte IO IDs, no NX/Generation Type)
- Codec 8 Extended parser (2-byte IO IDs + variable-length NX section)
- Codec 16 parser (mixed widths + Generation Type, supports IO IDs > 255)
- Shared GPS element / timestamp helpers in gps-element.ts
- Fixture loader with bigint/Buffer sentinel encoding and auto-discovery
- 12 fixture pairs across codec8/8E/16 (canonical doc + synthetic edge cases)
- Cross-checked Codec 8 against Traccar's TeltonikaProtocolDecoder (no discrepancies)

26 new tests. Total 62 passing across 10 test files.
typecheck/lint/test/build all clean.

test/fixtures/teltonika/codec8e/02-nx-mixed.expected.json

@@ -0,0 +1,22 @@
+{
+  "positions": [
+    {
+      "device_id": "FIXTURE",
+      "timestamp": "2019-06-10T10:04:46.000Z",
+      "latitude": 0,
+      "longitude": 0,
+      "altitude": 0,
+      "angle": 0,
+      "speed": 0,
+      "satellites": 0,
+      "priority": 1,
+      "attributes": {
+        "__event": 0,
+        "1": "__buffer_b64:qw==",
+        "2": "__buffer_b64:3q2+7wECAwQ=",
+        "3": "__buffer_b64:YWJjZGVmZ2hpamtsbW5vcHFyc3R1dnd4eXp7fH1+f4CBgoOEhYaHiImKi4yNjo+QkZKTlJWWl5iZmpucnZ6foA=="
+      }
+    }
+  ],
+  "ack_record_count": 1
+}