added test for writable folders

[alexlib]

• due to failure on Windows without any warning for Read-only folders
• added Python checks and warnings and errors in the terminal instead of crash

[Copilot]

Pull request overview

This PR adds preflight checks to ensure output directories are writable (especially on Windows), and updates tests to cover the new behavior so write failures produce actionable errors rather than silent/unclear failures.

Changes:

• Add output-path preparation + writable-directory probing helpers in pyptv.ptv, and use them before writing targets/correspondence outputs.
• Add GUI-side res/ directory creation/writability validation during initialization.
• Update and expand tests to validate directory creation, probing, and error behavior.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 4 comments.

File	Description
pyptv/ptv.py	Adds output path prep / write error helpers, probes target output dirs before writes, and routes write failures through actionable exceptions.
pyptv/pyptv_gui.py	Ensures res/ exists and is writable during GUI init to avoid later failures when writing outputs.
tests/test_ptv_file_io.py	Updates target-write tests to use real filesystem temp paths and adds coverage for new helper functions + preflight call.
tests/test_gui_output_directory.py	Adds tests for GUI res/ directory creation, warnings, and permission-error handling.

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[Copilot]

@alexlib I've opened a new pull request, #106, to work on those changes. Once the pull request is ready, I'll request review from you.

[Copilot]

@alexlib I've opened a new pull request, #107, to work on those changes. Once the pull request is ready, I'll request review from you.

[Copilot]

@alexlib I've opened a new pull request, #108, to work on those changes. Once the pull request is ready, I'll request review from you.