DASP: drop the P-ION resend overrides, use standard 512-byte packets

The save and file-open requests used their own fixed resend intervals
(5 s / 15 s) and the hello asked for 256-byte packets. Ontrol's Sedona
Java stack does neither and works with the P-ION: the standard backoff
(1, 2, 4, 8 s) sends a busy device a few copies with the same seqNum,
which its receive window drops. Both are removed.

Also fixes a race in SendWindow.send(): the packet entered the window
before its payload and sent_time were set, so housekeeping could resend
it with an empty payload, and the device would then drop the real one
as a duplicate.

Tested on a P-ION at 192.168.1.252, App > Get with File: save 3.2 s
(2 resends), app.sab + kits.scode in 11.3 s with 500-byte chunks
(was 14.6 s at 256), device stayed up, files identical to a 256-byte
backup.

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

app_backup.py

@@ -23,7 +23,6 @@ import zipfile
 
 import app_state
 import sab_app
-import sox
 from ox_widget_properties import IMAGE_EXTENSIONS, ORION_KIT, RION_KIT
 
 APP_SAB = "app.sab"
@@ -163,14 +162,12 @@ def _source_entry(media, source_path):
 def save_app(client):
     """Invokes App.save on the device and waits for it to finish.
 
-    Ontrol's Niagara driver does this before every app.sab get, resending the request
-    only every 5 s: a P-ION saving a large app takes seconds, and 1 s resends of the
-    request while it is busy are what knocked it over.
+    Ontrol's Niagara driver does this before every app.sab get.
     """
     comp = client.cache_get(0) or client.load(0)
     slots = client.slot_registry.get((comp.kit_id, comp.type_id)) or []
     slot = next((s for s in slots if s["name"] == "save" and s.get("is_action")), None)
-    client.invoke(0, slot["id"] if slot else 0, send_retry=sox.SAVE_SEND_RETRY)
+    client.invoke(0, slot["id"] if slot else 0)
 
 
 class BackupResult: