feat: implementation of setModeNamed to specify keyboard modes

[luizfern12]

Description

Added setModeNamed(String modeName) to allow switching to a specific keyboard mode by its key name. This implementation includes a check to prevent redundant rebuilds if the requested mode is already active and validates the mode existence within the current layout.

This feature improves efficiency in UI flows where specific input types require immediate access to a particular keyboard layout (e.g., jumping directly to a numeric pad for currency input).

Type of change

• New feature (non-breaking change which adds functionality)

How Has This Been Tested?

• Verified that the new method correctly updates the keyboard state in a local environment.
• Ran the provided example app to ensure no regressions in existing switchMode() behavior.
• Tested a modified version of the example invoking setModeNamed('numeric') from an external trigger with a custom keyboard layout.

Test Configuration:

• Flutter SDK: 3.38.9
• Operating System: Linux 6.18.6-arch1-1 (Arch Linux)

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• My changes generate no new warnings
• New and existing unit tests pass locally with my changes

[albinpk]

@luizfern12 Thanks for the contribution! This is a great addition