issue #493 fix for 128D and 128DCR

[slesinger]

Problem

Users of the 128D and 128DCR models have reported that the RETURN key feels unresponsive compared to other keys, causing typing frustration and affecting user experience when entering commands.

Solution

This PR implements special handling for the RETURN key on C128D and 128DCR models by:

• Adding dedicated logic to detect and process RETURN key presses differently
• Reducing the debounce delay specifically for the RETURN key
• Cutting the initial key delay in half for RETURN key presses (using first_delay / 2)
• Accelerating the delay counter decrement to make repeat presses more responsive
• Using half the standard repeat delay (using repeat_speed / 2) for subsequent RETURN key presses

Testing

The implementation has been tested on:

• C128D hardware
• C128DCR hardware
• Standard C64 to ensure no regressions

Related Issues

Fixes #493 - "Slow RETURN key response on 128D and 128DCR models"

[GideonZ]

Why does this help?