Phase 3 PR 51 -- DL260 X-input FC02 discrete-input mapping end-to-end test. Integration test DL205XInputTests reads FC02 at the DirectLogicAddress.XInputToDiscrete-resolved address and asserts two behaviors against the dl205.json pymodbus profile: (1) X20 octal (=decimal 16 = Modbus DI 16) reads ON, proving the helper correctly octal-parses the trailing number and adds it to the 0 base; (2) X21 octal reads OFF (not exception) -- per docs/v2/dl205.md §I/O-mapping, 'reading a non-populated X input returns zero, not an exception' on DL260, because the CPU sizes the discrete-input table to the configured I/O not the installed hardware. Pymodbus models this by returning the default 0 value for any DI bit in the configured 'di size' range that wasn't explicitly seeded, matching real DL260 behaviour. Test uses X20 rather than X0 to sidestep a shared-blocks conflict: pymodbus places FC01/FC02 bit-address 0..15 into cell 0, but cell 0 is already uint16-typed (V0 marker = 0xCAFE) per the register-zero quirk test, and shared-blocks semantics allow only one type per cell. X20 octal = DI 16 lands in cell 1 which is free, so both the V0 quirk AND the X-input quirk can coexist in one profile. dl205.json: bits cell 1 seeded value=9 (bits 0 and 3 set -> X20, X23 octal = ON), write-range extended to include cell 1 (though X-inputs are read-only; the write-range entry is required by pymodbus for ANY cell referenced in a bits section even if only reads are expected -- pymodbus validates write-access uniformly). 10/10 DL205 integration tests pass with MODBUS_SIM_PROFILE=dl205. No driver code changes -- the XInputToDiscrete helper + FC02 read path already landed in PRs 50 and 21 respectively. This PR closes the integration-test gap that docs/v2/dl205.md called out under test name DL205_Xinput_unpopulated_reads_as_zero.

tests/ZB.MOM.WW.OtOpcUa.Driver.Modbus.IntegrationTests/Pymodbus/dl205.json

@@ -36,6 +36,7 @@
         [1280, 1282],
         [1343, 1343],
         [1407, 1407],
+        [1, 1],
         [128, 128],
         [192, 192],
         [250, 250],
@@ -88,6 +89,9 @@
       ],
 
       "bits": [
+        {"_quirk": "X-input bank marker cell. X0 -> DI 0 conflicts with uint16 V0 at cell 0, so this marker covers X20 octal (= decimal 16 = DI 16 = cell 1 bit 0). X20=ON, X23 octal (DI 19 = cell 1 bit 3)=ON -> cell 1 value = 0b00001001 = 9.",
+         "addr": 1, "value": 9},
+
         {"_quirk": "Y-output bank marker cell. pymodbus's simulator maps Modbus FC01/02/05 bit-addresses to cell index = bit_addr / 16; so Modbus coil 2048 lives at cell 128 bit 0. Y0=ON (bit 0), Y1=OFF (bit 1), Y2=ON (bit 2) -> value=0b00000101=5 proves DL260 mapping Y0 -> coil 2048.",
          "addr": 128, "value": 5},