Refactor validator factory internals by responsibility

[imdhemy]

Summary

Split src/validator/factory/create-validator.ts into internal factory modules organized by responsibility, while keeping createValidator as the single public export.

Recommendation

Refactor the factory internals into focused modules such as:

• create-validator.ts: public factory only
• apply-field-schema.ts: recursive traversal, context building, nested schema execution
• normalize-field-schema.ts: schema normalization into [constraintName, options] tuples
• resolve-constraint.ts: registry lookup and UnknownConstraintError

The goal is to sharpen separation of concerns without changing runtime behavior or expanding the public API surface. Helper modules should remain internal to src/validator/factory.

Why

create-validator.ts currently owns multiple responsibilities at once:

• validator construction
• field schema traversal
• constraint resolution
• schema normalization

That makes the file the main accumulation point for validator design drag and increases the chance of DSL drift over time.

Constraints

• Keep createValidator as the only public factory export
• Keep helper modules internal to src/validator/factory
• Preserve runtime behavior
• Include cleanup only where it removes duplication or clarifies ownership
• Avoid opportunistic public API changes during the refactor