Feature request: %installer_id% template for --subdir-installers to separate builds into subdirectories

[rixxxxx]

Summary

When downloading games with --platform all --language all, GOG embeds the version string and a build ID in the filename (e.g. setup_game_1.20_gog_v3_(86337).exe).
When a new build is released (setup_game_1.20_gog_v4_(90542).exe), both files accumulate in the game directory.

For archival use cases this is intentional, but the directory becomes cluttered as builds accumulate across many games and languages.

Proposed solution

Add a new template %installer_version% to --subdir-installers (and the other --subdir-* options) that resolves to the version field already present in gameFile.version, with spaces replaced by underscores for filesystem compatibility.

Desired usage:

lgogdownloader --download --subdir-installers %installer_version%

Resulting structure:

rollercoaster_tycoon_deluxe/
├── 1.20_GOG_v3/
│   ├── setup_..._v3_(86337).exe
│   ├── setup_..._v3_(french)_(86337)-1.bin
│   └── ...
├── 1.20_GOG_v4/
│   ├── setup_..._v4_(90542).exe
│   └── ...
├── extras/
└── patches/

Investigation

Before proposing this, the API output was verified with --list details:

id: en1installer0
version: 1.20 GOG v4

id: de1installer0
version: 1.20 GOG v4

Key findings:

• gameFile.id contains a language/index string like de1installer0, so not the numeric build ID visible in filenames. It is not suitable as a grouping key.
• gameFile.version contains the human-readable version string (e.g. "1.20 GOG v4") and is identical across all language variants of the same build and making it the correct field for grouping.
• --check-orphans already uses recursive_directory_iterator internally, so no changes required there.

Compatibility requirements

• --repair must resolve the same subdir path --> should work automatically via shared path construction
• --check-orphans: files from older builds that are no longer available on GOG servers will be reported as orphans, so this is expected and correct behavior, not a regression.
• Default behavior (no %installer_version% in template) must remain unchanged.
• If gameFile.version is empty (not all games provide a version string), the template should either fall back gracefully or be documented as producing an empty path segment.

Questions for the maintainer (@Sude- )

1. Is gameFile.version the intended field for this use case, or is there a more stable/canonical identifier for grouping installer variants of the same build?
2. What is the preferred handling when gameFile.version is empty, sosilent fallback to root, a warning, or a configurable fallback string?
3. Would a PR be welcome, or is there a different preferred approach?