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_controller.py

@@ -0,0 +1,84 @@
+import time
+
+import pytest
+from bits import Bit
+
+from progpib.controller import GpibController
+from progpib.exceptions import CommandError
+
+
+def _wait_until(condition, timeout=2.0, interval=0.02):
+    deadline = time.monotonic() + timeout
+    while time.monotonic() < deadline:
+        if condition():
+            return True
+        time.sleep(interval)
+    return condition()
+
+
+def test_mode_property_roundtrip(fake_gpib_server):
+    server, tcp_server = fake_gpib_server
+    with GpibController.ethernet(tcp_server.host, tcp_server.port) as ctrl:
+        ctrl.mode = 1
+        assert ctrl.mode == 1
+        ctrl.mode = 0
+        assert ctrl.mode == 0
+
+
+def test_addr_property_roundtrip_as_tuple(fake_gpib_server):
+    server, tcp_server = fake_gpib_server
+    with GpibController.ethernet(tcp_server.host, tcp_server.port) as ctrl:
+        ctrl.addr = (5, 96)
+        assert ctrl.addr == (5, 96)
+        ctrl.addr = 12
+        assert ctrl.addr == 12
+
+
+def test_ver_returns_server_version(fake_gpib_server):
+    server, tcp_server = fake_gpib_server
+    with GpibController.ethernet(tcp_server.host, tcp_server.port) as ctrl:
+        assert ctrl.ver() == server.version
+
+
+def test_write_escapes_special_bytes_on_the_wire(fake_gpib_server):
+    server, tcp_server = fake_gpib_server
+    with GpibController.ethernet(tcp_server.host, tcp_server.port) as ctrl:
+        ctrl.write("*IDN?\r\n+test")
+        expected = b"*IDN?\x1b\r\x1b\n\x1b+test\n"
+        assert _wait_until(lambda: bytes(server.raw_received) == expected)
+
+
+def test_read_tmo_ms_range_validation_without_network(fake_gpib_server):
+    server, tcp_server = fake_gpib_server
+    with GpibController.ethernet(tcp_server.host, tcp_server.port) as ctrl:
+        with pytest.raises(ValueError):
+            ctrl.read_tmo_ms = 5000
+        # unchanged: the invalid value was never sent
+        assert ctrl.read_tmo_ms == 500
+
+
+def test_status_and_lon_raise_in_controller_mode(fake_gpib_server):
+    server, tcp_server = fake_gpib_server
+    server.state["mode"] = "1"  # CONTROLLER
+    with GpibController.ethernet(tcp_server.host, tcp_server.port) as ctrl:
+        with pytest.raises(CommandError):
+            _ = ctrl.status
+        with pytest.raises(CommandError):
+            _ = ctrl.lon
+
+
+def test_status_and_spoll_return_bits_with_rqs_at_index_6(fake_gpib_server):
+    server, tcp_server = fake_gpib_server
+    server.state["mode"] = "0"  # DEVICE
+    server.state["status"] = "72"  # 0x48: RQS (bit 6) and bit 3 set
+    server.spoll_response = 72
+
+    with GpibController.ethernet(tcp_server.host, tcp_server.port) as ctrl:
+        status = ctrl.status
+        assert int(status) == 72
+        assert status[6] == Bit(1)
+        assert status[5] == Bit(0)
+
+        result = ctrl.spoll()
+        assert int(result) == 72
+        assert result[6] == Bit(1)