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>

device_session.py

@@ -10,7 +10,6 @@ import xml.etree.ElementTree as ET
 
 import app_state
 import schema
-import sox
 from sox import SoxClient, SoxComponent, TREE, CONFIG, RUNTIME, LINKS, ALL
 
 
@@ -44,8 +43,7 @@ class DeviceSession:
 
     def connect(self, host, port, user, password):
         """DASP connect → read schema → load root. Called from background thread."""
-        self.sox_client = SoxClient(host, int(port), user, password,
-                                    ideal_max=sox.IDEAL_MAX, abs_max=sox.ABS_MAX)
+        self.sox_client = SoxClient(host, int(port), user, password)
         self.sox_client.on_event = self._on_sox_event
         self.sox_client.checksum_resolver = schema.resolve_truncated_checksum
         self.sox_client.connect()