fix(plugins): Python plugins see the host document again

Plugins read the host's document through a shared reference across the
dynamic-library boundary, and the entity index hashed with foldhash's
per-process seed, so every handle lookup from the plugin missed. The
codec now uses a fixed hasher (opencadcodec f385f75; kernel 9841749,
graph e9c23ad).

The Python IPC suite also caught up with intended changes: ATTDEF
renders its tag, DXF now keeps the lock-position flag, and the modify
audit turns associative arrays off since it checks loose copies.
The rate-limiter test waits for the host's check instead of a fixed
sleep that raced on macOS, and ENV_LOCK no longer cascades a poisoned
lock into every later test.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

plugins/opencad-python/Cargo.lock

@@ -1264,7 +1264,7 @@ dependencies = [
 [[package]]
 name = "opencadcodec"
 version = "0.6.0"
-source = "git+https://github.com/HakanSeven12/opencadcodec.git?rev=d36331d#d36331d9e4f01576cdd29e8420caeb6503675c2c"
+source = "git+https://github.com/HakanSeven12/opencadcodec.git?rev=f385f75#f385f75decc311b7caeefb22d4e7435d97e12edb"
 dependencies = [
  "anyhow",
  "bitflags",