feat: Add automated test suite for canvas_field_component

Martin Anderson-Clutzrequested to merge
issue/canvas_field_component-3587749:feat/automated-tests into 1.0.x

Adds Unit, Kernel, and Functional tests covering the module's main behaviours: type-coercion normalization, input/output conversion, field hydration and rendering, form building, validation, config schema registration, module install hooks, and the HTMX formatter section endpoint.

Co-Authored-By: Claude Sonnet 4.6 noreply@anthropic.com

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