feat(hyprland/submap): add config option to specify different icons for submaps

[szbmrk]

Summary

This PR adds support for configurable icons in the Hyprland submap module based on the active submap name.

New Configuration Options

• icons: Object mapping submap names to their corresponding icons/strings
  • Keys: submap names (e.g., "resize", "pause")
  • Values: icons or strings to display for those submaps
  • The selected icon is made available via the {icon} placeholder in the format string

Format String Changes

The format option now supports two placeholders:

• {submap}: The currently active submap name (replaces the legacy {} placeholder)
• {icon}: The icon associated with the current submap (from the icons configuration)
• having only {} will work the same as before and will show the submap name, so if anybody updates there will be no breaking changes for their configs

Example Configuration

"hyprland/submap": {
    "format": "{icon} {submap}",
    "max-length": 8,
    "tooltip": false,
    "icons": {
        "resize": "",
        "pause": "",
    }
}

Implementation Details

• Added icons_ map to store submap name to icon mappings
• Added icon_ member variable to track the current icon
• Icons are loaded from the configuration during module initialization
• The icon is updated dynamically when the submap changes
• If no icon is defined for a submap, the {icon} placeholder will be empty
• Legacy format string using {} is still supported for backward compatibility