feat(components): add visual checkbox component using shapes

[vamshi1188]

Introduces a new Checkbox component rendered using shapes instead of Unicode
characters or PDF form fields.

• Adds checkbox component and props
• Implements rendering in gofpdf provider
• Includes unit tests, examples, and golden tests
• Addresses issue Is there any way to add check boxes for gender selection or marital status selection #488

This component is visual-only by design and aligns with Maroto v2 layout philosophy.

Description

Maroto currently does not provide a native way to render checkbox-style
selections (e.g. gender, marital status). Unicode-based approaches are unreliable
due to font limitations, and interactive PDF form fields are outside Maroto’s
scope.

This PR introduces a deterministic, layout-safe Checkbox component implemented
using shapes and text, ensuring consistent rendering across PDF viewers while
respecting Maroto’s component-based design.

Related Issue

• Fixes Is there any way to add check boxes for gender selection or marital status selection #488

Checklist

• Wrote unit tests for new/changed features.
• Updated example_test.go.
• New public methods/structs/interfaces have comments explaining their responsibilities.

[johnfercher]

Thanks! I will merge it to a develop branch and then to master.

[johnfercher]

There is a problem with the implementation with the grid system: #552