use persistent names for data directory

[nivkner]

fixes #74 by using the v1 info hash of the torrent as a stable and unique identifier of the torrent.

[Copilot]

Pull Request Overview

This PR updates directory handling to use the torrent’s v1 info-hash as a stable identifier and ensures metadata’s info_hashes is populated before use.

• Modified populate_target to take a directory name and removed mkdtemp in favor of a deterministic subfolder.
• Ensured p.info_hashes is explicitly set after loading metadata.
• Refactored main to compute the v1 hash string, call populate_target, and set up p.save_path accordingly.

Comments suppressed due to low confidence (1)

src/btfs.cc:876

• The magnet-URI branch relies on parse_magnet_uri to populate info_hashes. Verify that info_hashes.v1 is always valid (or explicitly assign it) before using it for directory naming.

		p.info_hashes = p.ti->info_hashes();

[johang]

Sorry, just trying out some Github features...

[johang]

Thanks for the patch!