feat(physics): MotionInterpreter.GetMaxSpeed for InterpolationManager (L.3.1 Task 2)

Ports retail's CMotionInterp::get_max_speed (0x00527cb0). Returns
motion-table-derived max speed (m/s) for InterpretedState.ForwardCommand:
- RunForward:   RunAnimSpeed (4.0) × (InqRunRate ?? MyRunRate)
- WalkForward:  WalkAnimSpeed (3.12)
- WalkBackward: WalkAnimSpeed × 0.65 (BackwardsFactor from adjust_motion @ 0x00528010)
- otherwise:    0

Decomp note: Binary Ninja emits a spurious void return for x87 FPU-returning
functions; the actual float return is confirmed by both callers
(StickyManager::adjust_offset @ 0x00555430,
InterpolationManager::AdjustOffset @ 0x00555d52) which multiply the result
by 2.0 to produce a catch-up speed in m/s. The per-command switch is
consistent with get_state_velocity (0x00527d50) which uses the same constants.

Used by InterpolationManager.AdjustOffset in Task 5 as 2 × GetMaxSpeed().
Until Task 5 wires it, the method is unused — covered by 4 unit tests.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/AcDream.Core/Physics/MotionInterpreter.cs

@@ -932,6 +932,56 @@ public sealed class MotionInterpreter
         apply_current_movement(cancelMoveTo: false, allowJump: true);
     }
 
+    // ── CMotionInterp::get_max_speed (0x00527cb0) ─────────────────────────────
+
+    /// <summary>
+    /// Return the motion-table-derived max speed (m/s) for the current
+    /// <see cref="InterpretedMotionState.ForwardCommand"/>.
+    ///
+    /// <para>
+    /// <b>Retail reference (named-retail, 0x00527cb0):</b>
+    /// <c>CMotionInterp::get_max_speed</c> fetches the run rate via
+    /// <c>InqRunRate</c> (or falls back to <c>my_run_rate</c>) and returns
+    /// the result as a float from the x87 FPU stack (ST0). The Binary Ninja
+    /// decompiler emits a spurious <c>void</c> return type for x87-returning
+    /// functions — the actual return value is confirmed by the two callers:
+    /// <c>StickyManager::adjust_offset</c> (0x00555430) and
+    /// <c>InterpolationManager::AdjustOffset</c> (0x00555d52), both of which
+    /// multiply the result by 2.0 to produce a catch-up speed in m/s. With a
+    /// run rate of ~1.0 the catch-up would be 2.0 m/s — far too slow — so the
+    /// function must return the actual velocity (m/s), not a bare rate.
+    /// </para>
+    ///
+    /// <para>
+    /// The per-command switch mirrors <c>get_state_velocity</c>
+    /// (0x00527d50), which uses the same constants and the same
+    /// RunForward / WalkForward / WalkBackward branches, and the
+    /// <c>adjust_motion</c> (0x00527c0e) <c>BackwardsFactor = 0.65</c>
+    /// scaling confirmed at address 0x00528010.
+    /// </para>
+    ///
+    /// <para>
+    /// Used by <c>InterpolationManager.AdjustOffset</c> in L.3 Task 5
+    /// as <c>2 × GetMaxSpeed()</c> catch-up speed.
+    /// </para>
+    /// </summary>
+    public float GetMaxSpeed()
+    {
+        // Resolve current run rate: prefer WeenieObj.InqRunRate, fall back to MyRunRate.
+        // Mirrors the InqRunRate query at the top of CMotionInterp::get_max_speed.
+        float rate = MyRunRate;
+        if (WeenieObj is not null && WeenieObj.InqRunRate(out float queried))
+            rate = queried;
+
+        return InterpretedState.ForwardCommand switch
+        {
+            MotionCommand.RunForward   => RunAnimSpeed * rate,
+            MotionCommand.WalkForward  => WalkAnimSpeed,
+            MotionCommand.WalkBackward => WalkAnimSpeed * 0.65f, // BackwardsFactor @ adjust_motion 0x00528010
+            _                          => 0f,                    // idle / non-locomotion
+        };
+    }
+
     // ── private helper ────────────────────────────────────────────────────────
 
     /// <summary>