Add tilde (~) expansion support for home directory paths

[ExcitedHumvee]

Description

Implements tilde (~) expansion for home directory paths in qBittorrent configurations, addressing issue #17583.

This allows users to specify paths like ~/Downloads instead of hard-coded absolute paths like /home/username/Downloads, making configuration files portable across users and systems.

Changes Made

• Core Implementation:

  • Added Utils::Fs::expandTilde() function to handle ~ and ~/path expansion
  • Integrated tilde expansion in SessionImpl for save/download path handling
  • Added tilde expansion support for category save paths
  • Applied expansion both during settings loading and when paths are set

• Testing:

  • Added comprehensive test suite testtildeexpansion.cpp
  • Tests cover all supported patterns: ~, ~/path, absolute paths, relative paths, empty paths
  • All 17 tests pass (including 8 tilde expansion tests)

Features

• ✅ Supports ~ (home directory) and ~/path (home + subpath) patterns
• ✅ Maintains backward compatibility with existing absolute/relative paths
• ✅ Cross-platform support for Windows, macOS, and Linux
• ✅ Security conscious: ~username patterns explicitly not supported
• ✅ Automatic expansion during config loading and path setting

Use Cases Addressed

• Portable configurations: Users can share config files without user-specific paths
• Easier backup/restore: No need to edit paths when restoring settings
• Intuitive usage: Users can type ~/Downloads instead of /home/username/Downloads
• Cross-system compatibility: Same config works across different user accounts

Testing

# Run the specific test
make testtildeexpansion && ./test/testtildeexpansion

# Run full test suite  
make check

[github-actions]

This PR is stale because it has been 60 days with no activity. This PR will be automatically closed within 7 days if there is no further activity.

[ExcitedHumvee]

@Chocobo1 , I've addressed the feedback. Could you please take another look when you have a moment?