feat: add mask() method to input field components for masking library integration

[Copilot]

Summary

Adds a public .mask(callback) method to SmarkForm field components that provides a clean integration scaffold for input-masking libraries (like iMask.js) without adding any hard dependency.

Changes

src/types/input.type.js

mask(callback) method (added to the input class, inherited by number, date, time, datetime-local, color, etc.):

• Temporarily changes <input type> to "text" for any non-text input, because masking libraries like iMask.js require type="text". The original type is preserved in _originalType.
• Calls callback(targetFieldNode) with the raw DOM element as the sole argument — this is the integration point where the caller attaches iMask or any other library.
• Stores the callback's return value as _maskInstance.
• For singletons, delegates to the inner field component (so _maskInstance lives where export() reads it).
• Returns this for chaining.

_setTargetFieldValue() updated:

• Dispatches a synthetic input event on the element when a mask instance is active. This allows masking libraries to re-process the value when import() is called programmatically.

export() updated:

• When _maskInstance.unmaskedValue is defined, uses it as the raw value instead of nodeFld.value. This ensures that derived types (number, date, time, etc.) receive the raw unmasked string and can still apply their own semantic type conversion (e.g. Number("1234.56") → 1234.56 rather than Number("1,234.56") → NaN).

test/mask.tests.js (new)

13 Playwright test cases covering:

• Type change for number/date inputs; no-op for text inputs
• _originalType is stored correctly
• Callback receives the correct DOM element
• mask() returns this for chaining
• export() uses unmaskedValue when provided
• Number fields still export a JS number after masking
• Fallback to nodeFld.value when mask has no unmaskedValue (or returns null)
• Singleton delegation: _maskInstance lands on the inner field
• import() dispatches input event on masked fields (and does NOT dispatch it on unmasked fields)

Usage example (iMask.js)

const form = new SmarkForm(document.querySelector("body"));
await form.rendered;

const priceField = form.find("/price");
priceField.mask(node => IMask(node, {
    mask: Number,
    scale: 2,
    thousandsSeparator: ',',
    radix: '.',
}));
// form.export() will still return { price: 1234.56 } even though
// the visible value is "1,234.56"

Testing

All 284 existing tests continue to pass. All 13 new mask tests pass.