fix(focas): decode cnc_rdmacro dec_val at offset 6; vacant/fractional macros go Bad

The ODBM wire payload is [i32 mantissa][i16 length, a constant 10][i16 dec_val].
ReadMacroAsync read the decimal at offset 4, so every macro decoded without
failing but wrongly: the captured #500 = 1.0 (05 f5 e1 00 00 0a 00 08) published
0.01. FANUC normalises macros to a 9-significant-digit mantissa, so the error
was never small.

- dec_val is read at [6..7]; a payload < 8 bytes is refused, not guessed at.
- A vacant variable (dec_val 0xFFFF) publishes BadNoData, never a Good 0.
- Integer-typed tags get the exact whole value (integer arithmetic); a
  fractional macro on an integer tag is BadTypeMismatch, a whole value that
  does not fit the type BadOutOfRange. Float tags get mantissa / 10^dec.

Ported from the sister ignitionoee FOCAS driver v0.15.0 (Focas.Wire-013,
Focas-017/018); live vectors from Makino Z-34184 (31i-B, G431).
Adds a WireFixtures helper that loads the raw 31i-B captures in Fixtures/v3.

src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.FOCAS/FocasStatusMapper.cs

@@ -19,6 +19,14 @@ public static class FocasStatusMapper
     public const uint BadTimeout = 0x800A0000u;
     public const uint BadTypeMismatch = 0x80740000u;
 
+    /// <summary>
+    ///     The CNC answered, but its answer describes no usable value — a vacant macro variable, a
+    ///     position / meter record whose own scale envelope is undecodable, a field the control did
+    ///     not report. Distinct from a comms fault (the device is fine) and never a fabricated
+    ///     Good <c>0</c>.
+    /// </summary>
+    public const uint BadNoData = 0x809B0000u;
+
     /// <summary>
     ///     Map common FWLIB <c>EW_*</c> return codes. The values below match Fanuc's published
     ///     numeric conventions (EW_OK=0, EW_FUNC=1, EW_NUMBER=3, EW_LENGTH=4, EW_ATTRIB=7,