v1.7.0: spurious end-of-decode hardening + session-resilient start.sh

The decoder could end decode() early on an idle/busy live line; the frontend
symptom was a flood of "sr_session_stop: session was NULL" after the session
stopped.  Harden the EOF detection and stop the capture from dropping.

pd.py:
- _at_eof(): a step that consumes only queued bytes (_replay / peeked_byte,
  e.g. the invalid-INS re-frame) no longer counts as end-of-capture; bounded
  to 64 consecutive no-advance steps.
- _stall_check(track=False): the idle-LEVEL wait in wait_data_falling returns
  immediately at the same sample on an idle line -- not EOF.  Only "pins is
  None" ends the wait there; sample-stall detection is kept for the edge wait.
- resync_idle(): guard wait()==None (was an unguarded pins[...] TypeError at
  stream end).

Effect: samsung_phone_sample.sr had halted at ~21.9M/320M samples with 1 APDU;
it now decodes through ~293M to a true end (939 APDUs, CHKSUM 176).  The 6
CONCAT packets are real mis-framed STK bursts now reachable (known Samsung
de-concatenation family).  All other traces unchanged.

start.sh:
- Auto-restart is now the default (--no-loop disables) so an intermittent
  FX2 USB stop reconnects instead of ending the session.
- Per-session pcap suffix (FILE.N.ext) so a restart never overwrites the
  previous capture.
- Filter the repetitive "sr_session_stop: session was NULL" teardown line
  from stderr (real decoder errors still pass).

Validation: test_8 56/0/OK, test_7 65/0/OK, xiaomi_phone 640, xiaomi_cold
473, 4gmodem 327, A55 407/395, S21p 399/375, target S21p 369; 0 CONCAT;
65/65 unit tests (10 new).  VERSION -> 1.7.0.

README.md

@@ -192,11 +192,16 @@ is the usual suspect.
 `start.sh` captures a continuous stream at the configured rate (default 16
 MHz) until Ctrl+C (`rc=130`). A healthy capture never ends by itself; if the
 FX2 drops the USB transfer mid-session (a flaky device, `rc=0` "device
-stopped streaming"), pass `--loop` to auto-restart — it re-launches the
-capture on every `rc=0` until you press Ctrl+C or hit `--max-restarts=N`
-(default 20; `0` = unlimited), with a `--restart-delay=S` gap (default 2 s).
+stopped streaming"), the capture auto-restarts so the session is not lost —
+it re-launches on every `rc=0` until you press Ctrl+C or hit
+`--max-restarts=N` (default 20; `0` = unlimited), with a `--restart-delay=S`
+gap (default 2 s). When restarting with `--pcap=FILE`, each session's capture
+is written to `FILE.<N>.<ext>` so a restart never overwrites the previous one,
+and the repetitive `sr_session_stop: session was NULL` teardown line is
+filtered from stderr.
 
-- `--loop` auto-restarts the capture when it ends on its own (`rc=0`).
+- `--no-loop` disables auto-restart (single capture only).
+- `--loop` forces auto-restart on (this is the default).
 - `--max-restarts=N` caps restarts (default 20; `0` = unlimited).
 - `--restart-delay=S` seconds to wait between restarts (default 2).
 - `--log` captures the `rc=` verdict line for the session end.