Add methods to query HeightMap values and statistics:
- get(pos): Get height value at integer coordinates
- get_interpolated(pos): Get bilinearly interpolated height at float coords
- get_slope(pos): Get slope angle (0 to pi/2) at position
- get_normal(pos, water_level): Get surface normal vector
- min_max(): Get (min, max) tuple of all values
- count_in_range(range): Count cells with values in range
All methods include proper bounds checking and error messages.
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
