Custom guides support and refactor of snapping and distance guides plugins

[jesusmpc]

Description

Refactor the current snapping and distance guide plugin to support custom guide sources, improve extensibility, and unify guide rendering/calculation logic across viewport, objects, and user-defined guides.

The current implementation tightly couples snapping logic with built-in stage/object bounds and makes it difficult to:

• introduce custom alignment guides,
• extend snapping behavior,
• reuse guide calculations,
• or support more advanced layout workflows.

This refactor should introduce a modular guide architecture that supports:

• built-in guides,
• custom guides,
• configurable snapping rules,
• and reusable distance/visibility calculations.

Goals

1. Custom Guide Support

Allow consumers to register custom guides dynamically.

Examples:

• canvas center lines,
• layout grids,
• safe areas,
• artboard margins,
• ruler guides,
• user-created alignment lines,
• section/container boundaries.

Custom guides should:

• participate in snapping,
• optionally render as visual guides,
• support horizontal and vertical directions,

2. Refactor Snapping Engine

Decouple snapping calculations from rendering and node traversal. Also unify snapping in a single central point.

Current issues:

• duplicated guide calculations,
• viewport/object snapping mixed together,
• difficult to extend snapping targets,
• inconsistent snapping resolution,
• limited composability.

The refactor should:

• normalize all guides into a shared structure,
• centralize snapping resolution,
• support multiple guide providers,
• simplify future feature additions.

3. Unified Distance Guide System

Distance guides should use the same guide infrastructure as snapping.

Requirements:

• shared bounding-box visibility calculations,
• reusable overlap/intersection utilities,
• viewport-aware guide rendering,
• support partially visible objects,
• predictable priority resolution.

Distance calculations should work consistently with:

• transformed nodes,
• zoom/pan,
• rotated groups,
• clipped viewport intersections.

Expected Outcome

After refactor:

• snapping becomes provider-based and extensible,
• custom guides are first-class citizens,
• distance guides reuse shared geometry logic,
• viewport visibility handling is consistent,
• and future guide-related features become easier to implement and maintain.