Extend wrmath to match Rust library in astro-rs

Brings the C++ library in line with the Rust wrmath crate in astro-rs,
which extends this library with additional geometry and estimation
primitives. All changes generated with AI assistance (Claude Fable 5).

New headers:
- wrmath/geom/matrix.h: Matrix<T,M,N> with rank, det, inv, transpose,
  and matrix-vector/matrix-matrix multiplication
- wrmath/geom/coord2d.h: Polar<T> 2D polar coordinates with navigation
  convention (clockwise-positive heading)
- wrmath/geom/coord3d.h: Spherical<T> 3D spherical coordinates with
  yaw/pitch, slerp, great-circle path interpolation, and quaternion
  direction
- wrmath/estim/imu.h: IMU<T> for 6-DoF and 9-DoF (MARG) sensor fusion

Extensions to existing headers:
- math.h: Epsilon3/6/Max constants; AbsTolerance (NaN/inf-safe),
  AbsError, RotateRadians, Circumference
- vector.h: zero(), withEpsilon(), asArray(), fromArray/Eps(), map(),
  isNaN(), angle2() (signed), euclidist(), projectLower/Tail<M>(),
  x()/y()/z() accessors; fixed isParallel() to use unit-vector equality
  (matches Rust fix for macOS/arm64 acos domain issue)
- quaternion.h: lerp(), slerp() methods; jacobian() returning
  Matrix<T,3,4>; direction()
- filter/madgwick.h: beta gain field, setDeltaT(), setGain(),
  direction(), updateFrame2(), updateAngularOrientation2()
- orientation.h/.cc: RBearing3d/f, ABearing3d/f, CompassHeading3d/f

Infrastructure:
- C++ standard bumped to C++17 (required for std::optional)
- CMake include path fixed so source-relative includes work
- Umbrella headers (geom.h, filter.h) updated

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

test/orientation_test.cc

@@ -1,7 +1,7 @@
 #include <gtest/gtest.h>
-#include <wrmath/math.h>
-#include <wrmath/geom/vector.h>
-#include <wrmath/geom/orientation.h>
+#include "wrmath/math.h"
+#include "wrmath/geom/vector.h"
+#include "wrmath/geom/orientation.h"
 
 using namespace std;
 using namespace wr;