android: add ability to launch digital assistant on long press

[kavishdevar]

This pull request refactors the codebase by reorganizing constants, improving modularity, and enhancing the PressAndHoldSettings functionality. The most significant changes include moving constants from utils to a new constants package, adding logic for customizable long-press actions, and cleaning up unused imports and code.

Refactoring and Modularization:

• Moved constants like AirPodsNotifications, NoiseControlMode, and Battery from utils to a new constants package for better organization (android/app/src/main/java/me/kavishdevar/librepods/constants/Packets.kt, android/app/src/main/java/me/kavishdevar/librepods/constants/StemAction.kt) [1] [2].
• Removed unused constants and enums from the Packets file during the refactor to streamline the codebase (android/app/src/main/java/me/kavishdevar/librepods/constants/Packets.kt).

Enhancements to PressAndHoldSettings:

• Added logic to retrieve and display user-configurable long-press actions for AirPods stems using SharedPreferences. This includes support for actions like "Cycle Noise Control Modes" and "Digital Assistant" (android/app/src/main/java/me/kavishdevar/librepods/composables/PressAndHoldSettings.kt) [1] [2] [3].
• Introduced a new StemAction enum to define possible long-press actions (android/app/src/main/java/me/kavishdevar/librepods/constants/StemAction.kt).

Import Cleanup:

• Removed redundant imports and adjusted import paths to reflect the new constants package structure across multiple files (e.g., MainActivity.kt, QuickSettingsDialogActivity.kt, and BatteryView.kt) [1] [2] [3].

Minor Functional Updates:

• Added a new bleOnlyMode setting in AirPodsSettingsScreen to support BLE-only mode configuration (android/app/src/main/java/me/kavishdevar/librepods/screens/AirPodsSettingsScreen.kt).

These changes improve code maintainability, enhance user customization options, and align with best practices for modularization.

^^ obviously ai :]