Refactor/code cleanup (#37)

* fix imports
remove unused imports
use full import path
sort import (1. Standard Library, 2. Third-Party, 3. Local) in alphabetic.

* - remove: Method 3 from src.core.ytsage_downlader:cleanup_subtitle_file
  - it could delete the subtitle file of other movies if it present in same directory as it scane recursively.

- refactor: migrate from os.path to pathlib.Path for path handling
  - Replaced os.path methods with pathlib.Path to improve readability,
  - avoid repeatation.
  - cross-platform compatibility, and maintain cleaner code.

- improve: enhance code readability
  - Standardized string literals to use double quotes for consistency
  - Removed unnecessary spaces to maintain cleaner formatting
  - Applied code formatting for better readability and maintainability

* - add: ytsage_constants.py file for one place to store all constants.

- imporve: return type hint for function.

- remove: src/gui/ytsage_gui_dialogs.py file to avoid repetation
  - src/gui/dialogs is renamed to src/gui/ytsage_gui_dialogs for same naming convection. (future import will remains same)
  - use of src/gui/ytsage_gui_dialogs/__init__.py to import the dilogs modules.

- change: variable self.parent to self._parent so it does not overwrite the parent()
  - add type hint checking.

* - refactor: QMetaObject.invokeMethod to Signal
  - I encounter error with incokeMethod. Could not solve it.
  - So, Changed it to Signal to match app code language.

- implement: the ytsage_constants.py to code
  - remove: unnecessary logic
  - remove: repetitive code logic.

- update: yt-dlp logic for src\gui\ytsage_gui_dialogs\ytsage_dialogs_update:_update_binary
  - yt-dlp update logic will use `yt-dlp -U`

* refactor: remove unused imports and streamline code formatting across multiple files

src/utils/ytsage_constants.py

@@ -0,0 +1,102 @@
+"""
+This module defines centralized constants used across the YTSage application.
+By storing shared values in one place, it improves consistency, readability,
+and maintainability of the codebase.
+
+Constants include:
+- Asset paths for icons and notification sounds.
+- OS detection and platform-specific directory paths for application data, binaries, logs, and configuration.
+- Download URLs for yt-dlp and ffmpeg binaries.
+- SUBPROCESS_CREATIONFLAGS: Used to specify subprocess creation flags (e.g., subprocess.CREATE_NO_WINDOW on Windows to hide the console window).
+Directories are automatically created when the module is imported, ensuring the required structure exists for the application.
+YTSage application constants.
+
+"""
+
+import os
+import platform
+import subprocess
+from pathlib import Path
+
+# Assets Constants
+ICON_PATH: Path = Path("assets/Icon/icon.png")
+SOUND_PATH: Path = Path("assets/sound/notification.mp3")
+
+OS_NAME: str = platform.system()  # Windows ; Darwin ; Linux
+
+USER_HOME_DIR: Path = Path.home()
+
+# OS Specific Constants
+if OS_NAME == "Windows":
+    OS_FULL_NAME: str = f"{OS_NAME} {platform.release()}"
+
+    # APP_PATH will be from system environment path or fallback to Path.home()
+    APP_DIR: Path = Path(os.environ.get("LOCALAPPDATA", USER_HOME_DIR / "AppData" / "Local")) / "YTSage"
+    APP_BIN_DIR: Path = APP_DIR / "bin"
+    APP_DATA_DIR: Path = APP_DIR / "data"
+    APP_LOG_DIR: Path = APP_DIR / "logs"
+    APP_CONFIG_FILE: Path = APP_DATA_DIR / "ytsage_config.json"
+
+    YTDLP_DOWNLOAD_URL: str = "https://github.com/yt-dlp/yt-dlp/releases/latest/download/yt-dlp.exe"
+    YTDLP_APP_BIN_PATH: Path = APP_BIN_DIR / "yt-dlp.exe"
+
+    SUBPROCESS_CREATIONFLAGS: int = subprocess.CREATE_NO_WINDOW
+
+elif OS_NAME == "Darwin":  # macOS
+    _mac_version = platform.mac_ver()[0]
+    OS_FULL_NAME: str = f"macOS {_mac_version}" if _mac_version else "macOS"
+
+    APP_DIR: Path = USER_HOME_DIR / "Library" / "Application Support" / "YTSage"
+    APP_BIN_DIR: Path = APP_DIR / "bin"
+    APP_DATA_DIR: Path = APP_DIR / "data"
+    APP_LOG_DIR: Path = APP_DIR / "logs"
+    APP_CONFIG_FILE: Path = APP_DATA_DIR / "ytsage_config.json"
+
+    YTDLP_DOWNLOAD_URL: str = "https://github.com/yt-dlp/yt-dlp/releases/latest/download/yt-dlp_macos"
+    YTDLP_APP_BIN_PATH: Path = APP_BIN_DIR / "yt-dlp"
+
+    SUBPROCESS_CREATIONFLAGS: int = 0
+
+
+else:  # Linux and other UNIX-like
+    OS_FULL_NAME: str = f"{OS_NAME} {platform.release()}"
+
+    APP_DIR: Path = USER_HOME_DIR / ".local" / "share" / "YTSage"
+    APP_BIN_DIR: Path = APP_DIR / "bin"
+    APP_DATA_DIR: Path = APP_DIR / "data"
+    APP_LOG_DIR: Path = APP_DIR / "logs"
+    APP_CONFIG_FILE: Path = APP_DATA_DIR / "ytsage_config.json"
+
+    YTDLP_DOWNLOAD_URL: str = "https://github.com/yt-dlp/yt-dlp/releases/latest/download/yt-dlp"
+    YTDLP_APP_BIN_PATH: Path = APP_BIN_DIR / "yt-dlp"
+
+    SUBPROCESS_CREATIONFLAGS: int = 0
+
+
+# ffmpeg download links
+FFMPEG_7Z_DOWNLOAD_URL = "https://github.com/GyanD/codexffmpeg/releases/download/7.1.1/ffmpeg-7.1.1-full_build.7z"
+FFMPEG_7Z_SHA256_URL = "https://www.gyan.dev/ffmpeg/builds/packages/ffmpeg-7.1.1-full_build.7z.sha256"
+FFMPEG_ZIP_DOWNLOAD_URL = "https://github.com/GyanD/codexffmpeg/releases/download/7.1.1/ffmpeg-7.1.1-full_build.zip"
+
+if __name__ == "__main__":
+    # If this file is run directly, print directory information; if imported, create the necessary directories for the application.
+    info = {
+        "OS_NAME": OS_NAME,
+        "OS_FULL_NAME": OS_FULL_NAME,
+        "USER_HOME_DIR": str(USER_HOME_DIR),
+        "APP_DIR": str(APP_DIR),
+        "APP_BIN_DIR": str(APP_BIN_DIR),
+        "APP_DATA_DIR": str(APP_DATA_DIR),
+        "APP_LOG_DIR": str(APP_LOG_DIR),
+        "APP_CONFIG_FILE": str(APP_CONFIG_FILE),
+        "YTDLP_DOWNLOAD_URL": YTDLP_DOWNLOAD_URL,
+        "YTDLP_APP_BIN_PATH": YTDLP_APP_BIN_PATH,
+        "SUBPROCESS_CREATIONFLAGS": SUBPROCESS_CREATIONFLAGS,
+    }
+    for key, value in info.items():
+        print(f"{key}: {value}")
+else:
+    APP_DIR.mkdir(parents=True, exist_ok=True)
+    APP_BIN_DIR.mkdir(parents=True, exist_ok=True)
+    APP_DATA_DIR.mkdir(parents=True, exist_ok=True)
+    APP_LOG_DIR.mkdir(parents=True, exist_ok=True)