Fixes #1370
Fixes #1493
Fixes #1238
Fixes #523 (as in we do re-import and delete the previous location)

This pull request refactors the directory import functionality by introducing a pipeline-based approach with modular processing stages. The changes aim to simplify the code, improve maintainability, and enhance functionality, such as tree-based album creation and better handling of reserved directories.

Refactoring of Exec class:

• Replaced the monolithic Exec class with a pipeline-based architecture for processing imports, using the Illuminate\Pipeline\Pipeline class. (app/Actions/Import/Exec.php)
• Introduced ImportDTO to encapsulate import parameters and state, replacing the use of multiple class properties. (app/Actions/Import/Exec.php)
• Removed legacy methods like normalizePath, readLocalIgnoreList, and checkAgainstIgnoreList, delegating these responsibilities to new pipeline stages. (app/Actions/Import/Exec.php)

New pipeline stages:

1. BuildTree:

   • Introduced the BuildTree pipeline stage to construct a tree structure of folders and files for import. (app/Actions/Import/Pipes/BuildTree.php)
   • Centralized path normalization and reserved directory checks within this stage. (app/Actions/Import/Pipes/BuildTree.php)

2. CreateNonExistingAlbums:

   • Added the CreateNonExistingAlbums stage to create albums for folders that do not already exist in the database. (app/Actions/Import/Pipes/CreateNonExistingAlbums.php)
   • Implemented a bottom-up approach to ensure child albums are processed before their parents. (app/Actions/Import/Pipes/CreateNonExistingAlbums.php)

Improvements to reserved directory handling:

• Consolidated reserved directory checks into a reusable folder_skip_list array in the BuildTree stage. (app/Actions/Import/Pipes/BuildTree.php)
• Improved error handling for invalid or reserved directories. (app/Actions/Import/Pipes/BuildTree.php)

These changes significantly enhance the modularity and readability of the import process while laying the groundwork for future extensibility.