Auto: s7-a3 — DTL/DT/S5TIME/TIME/TOD/DATE codecs

Adds S7DateTimeCodec static class implementing the six Siemens S7 date/time
wire formats:

  - DTL (12 bytes): UInt16 BE year + month/day/dow/h/m/s + UInt32 BE nanos
  - DATE_AND_TIME (8 bytes BCD): yy/mm/dd/hh/mm/ss + 3-digit BCD ms + dow
  - S5TIME (16 bits): 2-bit timebase + 3-digit BCD count → TimeSpan
  - TIME (Int32 ms BE, signed) → TimeSpan, allows negative durations
  - TOD (UInt32 ms BE, 0..86399999) → TimeSpan since midnight
  - DATE (UInt16 BE days since 1990-01-01) → DateTime

Mirrors the S7StringCodec pattern from PR-S7-A2 — codecs operate on raw byte
spans so each format can be locked with golden-byte unit tests without a
live PLC. New S7DataType members (Dtl, DateAndTime, S5Time, Time, TimeOfDay,
Date) are wired into S7Driver.ReadOneAsync/WriteOneAsync via byte-level
ReadBytesAsync/WriteBytesAsync calls — S7.Net's string-keyed Read/Write
overloads have no syntax for these widths.

Uninitialized PLC buffers (all-zero year+month for DTL/DT) reject as
InvalidDataException → BadOutOfRange to operators, rather than decoding as
year-0001 garbage.

S5TIME / TIME / TOD surface as Int32 ms (DriverDataType has no Duration);
DTL / DT / DATE surface as DriverDataType.DateTime.

Test coverage: 30 new golden-vector + round-trip + rejection tests,
including the all-zero buffer rejection paths and BCD-nibble validation.
Build clean, 115/115 S7 tests pass.

Closes #289

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/ZB.MOM.WW.OtOpcUa.Driver.S7/S7DriverOptions.cs

@@ -123,4 +123,16 @@ public enum S7DataType
     /// <summary>S7 WCHAR: two bytes UTF-16 big-endian.</summary>
     WChar,
     DateTime,
+    /// <summary>S7 DTL — 12-byte structured timestamp with year/mon/day/dow/h/m/s/ns; year range 1970-2554.</summary>
+    Dtl,
+    /// <summary>S7 DATE_AND_TIME (DT) — 8-byte BCD timestamp; year range 1990-2089.</summary>
+    DateAndTime,
+    /// <summary>S7 S5TIME — 16-bit BCD duration with 2-bit timebase; range 0..9990s. Surfaced as Int32 ms.</summary>
+    S5Time,
+    /// <summary>S7 TIME — signed Int32 ms big-endian. Surfaced as Int32 ms (negative durations allowed).</summary>
+    Time,
+    /// <summary>S7 TIME_OF_DAY (TOD) — UInt32 ms since midnight big-endian; range 0..86399999. Surfaced as Int32 ms.</summary>
+    TimeOfDay,
+    /// <summary>S7 DATE — UInt16 days since 1990-01-01 big-endian. Surfaced as DateTime.</summary>
+    Date,
 }