sx-git extension: git-wire import — the inverse adapter, round-trip law (TDD)

lib/git/import.sx parses loose payloads back to native objects bottom-up
over an export-set table: tree mode/name/raw-sha triples, ident lines,
header/message split, committer stored only when distinct so export
defaults regenerate identical bytes. Laws verified: export->import->export
is BYTE-IDENTICAL (head sha + every object), imported blobs/default-mode
trees regain their original native cids, 100755/tags/distinct-committer/
multi-line messages all survive. 15/15, total 267/267.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

lib/git/scoreboard.json

@@ -7,9 +7,10 @@
     "diff": {"pass": 27, "fail": 0},
     "merge": {"pass": 28, "fail": 0},
     "porcelain": {"pass": 40, "fail": 0},
-    "export": {"pass": 25, "fail": 0}
+    "export": {"pass": 25, "fail": 0},
+    "import": {"pass": 15, "fail": 0}
   },
-  "total_pass": 252,
+  "total_pass": 267,
   "total_fail": 0,
-  "total": 252
+  "total": 267
 }