fix(focas-tests): honour fixture endpoint + fix mock timer endianness (9F/1P -> 10/10)

Two test/fixture bugs; NO OtOpcUa driver change.

1. Topology: FocasSimFixture reads an env-overridable endpoint
   (OTOPCUA_FOCAS_SIM_ENDPOINT, default localhost:8193) and exposes Host/Port,
   but WireBackendTests + WireBackendCoverageTests hardcoded
   focas://127.0.0.1:8193. Against a remote fixture the skip-gate passed
   (remote reachable) but the driver dialed localhost -> KeyNotFound. Added a
   DeviceUri property to the fixture; each test now derives DeviceHost from it.
   Recovered 8 of 9.

2. Mock timer endianness (surfaced once #1 let the tests reach the mock): the
   last failure read 60397977600 for a 3600 s power-on timer (= 0x3C000000 x 60).
   The focas-mock's _wire_timer encoded the minute/msec fields big-endian (_u32),
   but cnc_rdtimer's timer fields are LITTLE-endian on real hardware — a
   documented, live-31i-B-validated quirk that FocasWireClient.ParseTimer decodes
   LE (docs/plans/2026-06-25-focas-pdu-v3-30i-b-support.md). The driver was
   correct; the mock was wrong. _wire_timer now emits little-endian (_u32_le).

Suite 9F/1P -> 10/10 against the remote fixture at ~/otopcua-focas.
Integration-sweep follow-up #3.

tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.IntegrationTests/Docker/focas-mock/src/focas_mock/server.py

@@ -415,7 +415,12 @@ class FocasMockServer:
         timer_type = self._block_u32(request_block, 8)
         key_map = {0: "power_on", 1: "operating", 2: "cutting", 3: "cycle"}
         seconds = int(self.store.snapshot()["timers"].get(key_map.get(timer_type, "power_on"), 0))
-        return self._u32(seconds // 60) + self._u32((seconds % 60) * 1000)
+        # cnc_rdtimer's minute+msec fields are LITTLE-endian on the wire — unlike the big-endian
+        # block envelope and every other payload. Hardware-validated against a live FANUC 31i-B
+        # (2026-06-25); the driver's FocasWireClient.ParseTimer decodes them little-endian. Encoding
+        # them big-endian here (the old bug) made the driver read minute=60 as 0x3C000000. See
+        # docs/plans/2026-06-25-focas-pdu-v3-30i-b-support.md.
+        return self._u32_le(seconds // 60) + self._u32_le((seconds % 60) * 1000)
 
     def _wire_alarms(self, request_block: bytes) -> bytes:
         requested = max(self._block_u32(request_block, 12), 1)
@@ -481,6 +486,11 @@ class FocasMockServer:
     def _u32(self, value: int) -> bytes:
         return int(value).to_bytes(4, "big", signed=True)
 
+    def _u32_le(self, value: int) -> bytes:
+        # Little-endian u32 — only cnc_rdtimer's minute/msec fields use this on real hardware
+        # (see _wire_timer). Every other wire field is big-endian via _u32.
+        return int(value).to_bytes(4, "little", signed=True)
+
     def _ascii_fixed(self, value: str, length: int) -> bytes:
         return value.encode("ascii", errors="replace")[:length].ljust(length, b" ")