fix: emit wire-shaped TPDUs in the GSMTAP stream (v3.1.1)

The GSMTAP stream sent logical APDUs, so a receiver (SIMtrace Analyser,
Wireshark) flagged almost every packet: case-4 commands carried their Le
byte ('length_mismatch: excessive') and responses were headerless packets
decoded as bogus commands ('truncated').  The ATR also arrived in the
middle of the stream.

- gsmtap.py: the tracer now emits wire-shaped TPDUs, matching a hardware
  sniffer capture: case 4 -> the command without Le plus the 61XX 'bytes
  available' SW (derived from the real response length), then the data as
  a GET RESPONSE TPDU (00C00000<len> + data + SW, chunked at 255); case
  1/2/3 -> one packet cmd + data + SW; unparseable APDUs fall back to raw
  command/response packets.
- No ATR/VCC/RST/PPS events at all (no line-level access over PC/SC);
  the ATR sending helper and the server-side plumbing were removed.
- Verified by replaying the bad capture's exchanges through the new
  tracer: 116 packets, zero decoder warnings (previously nearly all).
- tests: the per-case wire forms, chunking, fallbacks; README/AGENTS
  document the wire shape and its limits; version 3.1.1, sw simple-v236.

pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "setuptools.build_meta"
 
 [project]
 name = "pysim-simple-server"
-version = "3.1.0"
+version = "3.1.1"
 description = "HTTP REST server wrapping pysim for the SIMple PWA"
 requires-python = ">=3.8"
 # pysim is a git-only dependency installed explicitly by setup.bat/setup.sh.