Update FieldUtil.kt

[TheChii]

Key Improvements:

Precise Field Dimensions:

Changed to Double type for accuracy

Added default constants with JVM static fields

Made field dimensions customizable while maintaining defaults

Safe Canvas Handling:

Added validation for positive canvas dimensions

Created dedicated setter method for canvas dimensions

Added runtime checks for proper initialization

Accurate Coordinate Conversion:

Fixed aspect ratio handling with proper per-axis scaling

Clear separation of screen and field coordinate systems

Added documentation about coordinate system assumptions

Improved Scaling Logic:

Unified scale calculation maintains aspect ratio

inchesToPixels now uses aspect-ratio-correct scaling

Removed unnecessary mirroring functions

Code Quality:

Meaningful method names (screenToField instead of screenCoordsToFieldCoords)

Proper JVM annotations for Java interoperability

Clear documentation explaining coordinate systems

Validation for invalid canvas states

Error Prevention:

Added input validation for canvas dimensions

Private setters for canvas dimensions to prevent accidental modification

Runtime checks ensure proper initialization before conversion