Replace progpib.py stub with a proper installable package

Builds a modern, testable API for the Prologix GPIB-ETHERNET controller
(GPIB-USB structurally supported but untested, no hardware available):
Transport abstraction (Ethernet now, serial later), GpibController for
the full "++" command set, a clean-room netfinder discovery client that
fixes a real chr()/struct-format bug present in vendortools/nfutil.py,
and a CLI (discover/config/info/terminal). vendortools/, pty-gpib-emulator/,
sampledata.txt and the manual PDF are kept untouched as reference material.

Depends on the sibling bits package (editable, not yet pinned -- see its
own commit) for MAC formatting and IEEE-488.2 status-byte bit access.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

tests/test_discovery_codec.py

@@ -0,0 +1,97 @@
+"""Pure, offline tests for the netfinder packet codec in progpib.discovery.
+
+Fixture bytes are taken from sampledata.txt, a captured Python 3 REPL
+session against real Prologix GPIB-ETHERNET hardware (all using the same
+sequence number, 30327 = 0x7677, reused across the whole session).
+"""
+
+from progpib.discovery import (
+    _HEADER_LEN,
+    DeviceInfo,
+    IpType,
+    NfCommand,
+    NfResult,
+    _pack_assignment,
+    _pack_header,
+    _pack_identify,
+    _unpack_assignment_reply,
+    _unpack_identify_reply,
+    _unpack_test_reply,
+)
+
+SEQ = 30327
+MAC = b"\x00!i\x01-\xaf"
+
+
+def test_pack_identify_matches_captured_bytes():
+    assert _pack_identify(SEQ) == b"Z\x00vw\xff\xff\xff\xff\xff\xff\x00\x00"
+
+
+def test_unpack_identify_reply_matches_captured_session():
+    reply = (
+        b"Z\x01vw\x00!i\x01-\xaf\x00\x00\x00%\x0572\x01\x00\x00\xc0\xa8\x00\xe5"
+        b"\xff\xff\xff\x00\xc0\xa8\x00\x01\x01\x06\x06\x00\x01\x03\x00\x00"
+        b"\x01\x03\x00\x00600" + b"\x00" * 29
+    )
+    assert len(reply) == 76
+    info = _unpack_identify_reply(reply)
+
+    assert info == DeviceInfo(
+        mac=MAC,
+        mode=1,
+        alert=0,
+        ip_type=IpType.DYNAMIC,
+        ip_address="192.168.0.229",
+        netmask="255.255.255.0",
+        gateway="192.168.0.1",
+        app_version="1.6.6.0",
+        boot_version="1.3.0.0",
+        hw_version="1.3.0.0",
+        name="600",
+        uptime_days=37,
+        uptime_hours=5,
+        uptime_minutes=55,
+        uptime_seconds=50,
+    )
+    assert info.mac_str == "00:21:69:01:2d:af"
+
+
+def test_pack_assignment_matches_captured_bytes():
+    # This regression-pins the chr()->bytes([...]) fix: vendortools/nfutil.py's
+    # MkAssignment raises struct.error on this exact call (see sampledata.txt),
+    # since struct.pack's 'c' format needs a length-1 bytes object, not chr()'s str.
+    packet = _pack_assignment(
+        SEQ,
+        MAC,
+        IpType.DYNAMIC,
+        "192.168.0.229",
+        "255.255.255.0",
+        "192.168.0.1",
+    )
+    expected = (
+        b"Z\x02vw\x00!i\x01-\xaf\x00\x00\x00\x00\x00\x00\xc0\xa8\x00\xe5"
+        b"\xff\xff\xff\x00\xc0\xa8\x00\x01" + b"\x00" * 32
+    )
+    assert len(expected) == 60
+    assert packet == expected
+
+
+def test_unpack_assignment_reply_matches_captured_bytes():
+    # This datagram is captured mid-session in sampledata.txt as a reply to
+    # an earlier Assignment request (both used seq 30327): header id 0x03 =
+    # ASSIGNMENT_REPLY, followed by a single 0x00 result byte = NF_SUCCESS.
+    reply = b"Z\x03vw\x00!i\x01-\xaf\x00\x00\x00\x00\x00\x00"
+    assert _unpack_assignment_reply(reply) == NfResult.SUCCESS
+
+
+def test_pack_and_unpack_test_reply_roundtrip():
+    # sampledata.txt has no clean captured TestReply (the byte string shown
+    # there after a MkTest() call is actually a stale AssignmentReply still
+    # sitting in the receive socket's buffer from an earlier command in that
+    # REPL session -- see test_unpack_assignment_reply_matches_captured_bytes
+    # above). So this is a synthetic round-trip instead of a captured fixture.
+    text = "Prologix GPIB-ETHERNET Sim 1.0"
+    body = text.encode("ascii").ljust(32, b"\x00")
+    reply = _pack_header(NfCommand.TEST_REPLY, SEQ, MAC) + body
+    assert len(reply) == _HEADER_LEN + 32
+    assert _unpack_test_reply(reply) == text