feat(datetime/picker): public API to programmatically enter numeric input mode

### Prerequisites

- [x] I have read the [Contributing Guidelines](https://github.com/ionic-team/ionic-framework/blob/main/docs/CONTRIBUTING.md#creating-an-issue).
- [x] I agree to follow the [Code of Conduct](https://ionicframework.com/code-of-conduct).
- [x] I have searched for [existing issues](https://github.com/ionic-team/ionic-framework/issues) that already include this feature request, without success.

### Describe the Feature Request

ion-datetime (wheel) + ion-picker supports a “numeric input mode” when the user taps a numeric column: the picker focuses an internal , shows the OS keypad, and lets users type to update both hour and minute columns.

There’s currently no public API to trigger the same behavior programmatically (e.g., from a button or accessibility shortcut).

### Describe the Use Case

- Accessibility: provide a keyboard/assistive-tech control to enter numeric mode.

- UX: offer an “Edit time” button that behaves exactly like a tap.

- Automated testing & consistency across platforms.

### Describe Preferred Solution

Expose a safe, documented method:

// on ion-picker (and used by ion-datetime internally)
enterInputMode(column?: HTMLIonPickerColumnElement | 'hour' | 'minute', options?: { focus?: boolean }): void;
exitInputMode(): void;

// or on ion-datetime (delegates to internal picker)
enterInputMode(scope?: 'all' | 'hour' | 'minute', options?: { focus?: boolean }): void;

Behavior should mirror a real tap:

- Set internal input-mode state (multi-column when scope === 'all').

- Emit the same event columns currently listen for.

- focus the hidden input to open the keypad.

### Describe Alternatives

_No response_

### Related Code

Any datetime/picker

### Additional Information

Without a public API, it’s impossible to trigger numeric input mode via assistive technology (e.g., VoiceOver/ TalkBack actions, hardware keyboard shortcuts, or custom accessibility buttons). This can prevent certain users from easily adjusting time values, especially those with motor impairments who find wheel scrolling difficult.