Add support for DE save_version 68

The mid-2026 Definitive Edition patch (build 101.103.48987 / 48086,
VER 9.4, save_version 68.0) changed the recorded-game header in two ways
relative to save_version 66.3/67:

1. Each player entry gained one trailing de_string field (observed empty).
2. The DE header block gained 8 trailing bytes just before the ai section.

Without these, the player array desyncs (ConstError on the next
de_string marker) and, once past that, has_ai is misread so the ai
skip-to-zero-run never fires and map_info lands in the string table.

Reverse-engineered from macOS (Feral) replays; verified against 5 games
across both build 48086 and 48987 via mgz.model.parse_match (header +
body + actions). Patches both the construct parser (header/de.py) and the
fast parser (fast/header.py, used by ModelSummary/parse_match), gated on
save_version >= 67.5 so 66.3/67 paths are untouched. Extends the
save-67 work in PRs happyleavesaoc#139/happyleavesaoc#142.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: CliveUnger

mgz/fast/header.py

@@ -470,6 +470,8 @@ def parse_de(data, version, save, skip=False):
             handicap = struct.unpack_from('<I', handicap_data, 4)[0]
         if save >= 64.3:
             data.read(4)
+        if save >= 67.5:
+            de_string(data)  # save_version 68: trailing per-player de_string
 
         players.append(dict(
             number=number,
@@ -556,6 +558,8 @@ def parse_de(data, version, save, skip=False):
         data.read(8)
         if save >= 37:
             timestamp, x = unpack('<II', data)
+        if save >= 67.5:
+            data.read(8)  # save_version 68: 8 trailing bytes before ai section
     rms_mod_id = None
     rms_filename = None
     for s in strings:

mgz/header/de.py

@@ -45,6 +45,8 @@
     "custom_ai"/Flag,
     If(lambda ctx: find_save_version(ctx) >= 25.06, "handicap"/Bytes(8)),
     If(lambda ctx: find_save_version(ctx) >= 64.3, "unknown_de_64_3" / Int32ul),
+    # save_version 68 (mid-2026 DE patch) added a trailing per-player de_string
+    "unknown_de_68"/If(lambda ctx: find_save_version(ctx) >= 67.5, de_string),
 )
 
 string_block = Struct(
@@ -178,5 +180,7 @@
     "ver37"/If(lambda ctx: find_save_version(ctx) >= 37, Struct(
         Int32ul,
         Int32ul
-    ))
+    )),
+    # save_version 68 (mid-2026 DE patch) added 8 trailing bytes before the ai section
+    If(lambda ctx: find_save_version(ctx) >= 67.5, Bytes(8)),
 )