feat: add Nix support for reproducible builds

[willyrgf]

Packaging the repository apps with Nix enables people to easily run these apps and extend them for other workflows.
A few tests pointing to my fork and commit (correct path if merged is in committed README.md):

# running gdformat nix run 'github:willyrgf/godot-gdscript-toolkit/4fe2a357831130d774f74942809577e7408f6742#gdformat' script.gd 0 files reformatted, 1 file left unchanged.

# running default app will show a helper ❯ nix run 'github:willyrgf/godot-gdscript-toolkit/4fe2a357831130d774f74942809577e7408f6742' GDScript Toolkit - Available commands: Usage: nix run github:Scony/godot-gdscript-toolkit#<command> -- [args] Available commands: gdparse - GDScript parser for debugging and educational purposes gdlint - GDScript linter that performs static analysis gdformat - GDScript formatter that formats code according to predefined rules gd2py - GDScript to Python transpiler gdradon - GDScript code complexity analysis (calculates cyclomatic complexity) Examples: nix run github:Scony/godot-gdscript-toolkit#gdformat -- --help nix run github:Scony/godot-gdscript-toolkit#gdlint -- myfile.gd nix run github:Scony/godot-gdscript-toolkit#gdparse -- myfile.gd -p For local development: nix develop # Enter development shell with all tools available

# all apps for --all-systems ❯ nix flake show 'github:willyrgf/godot-gdscript-toolkit/4fe2a357831130d774f74942809577e7408f6742' --all-systems github:willyrgf/godot-gdscript-toolkit/4fe2a357831130d774f74942809577e7408f6742?narHash=sha256-rtyKi7OtZrxfXUw55Gu8i5nvDGSPBH1Ycz5FAXJpThg%3D ├───apps │ ├───aarch64-darwin │ │ ├───default: app: Show available GDScript Toolkit commands │ │ ├───gdformat: app: GDScript formatter │ │ ├───gdlint: app: GDScript linter │ │ ├───gdparse: app: GDScript parser │ │ ├───gdradon: app: GDScript code complexity analysis │ │ └───help: app: Show available GDScript Toolkit commands │ ├───aarch64-linux │ │ ├───default: app: Show available GDScript Toolkit commands │ │ ├───gdformat: app: GDScript formatter │ │ ├───gdlint: app: GDScript linter │ │ ├───gdparse: app: GDScript parser │ │ ├───gdradon: app: GDScript code complexity analysis │ │ └───help: app: Show available GDScript Toolkit commands │ ├───x86_64-darwin │ │ ├───default: app: Show available GDScript Toolkit commands │ │ ├───gdformat: app: GDScript formatter │ │ ├───gdlint: app: GDScript linter │ │ ├───gdparse: app: GDScript parser │ │ ├───gdradon: app: GDScript code complexity analysis │ │ └───help: app: Show available GDScript Toolkit commands │ └───x86_64-linux │ ├───default: app: Show available GDScript Toolkit commands │ ├───gdformat: app: GDScript formatter │ ├───gdlint: app: GDScript linter │ ├───gdparse: app: GDScript parser │ ├───gdradon: app: GDScript code complexity analysis │ └───help: app: Show available GDScript Toolkit commands ├───devShells │ ├───aarch64-darwin │ │ └───default: development environment 'gdtoolkit-dev-env' │ ├───aarch64-linux │ │ └───default: development environment 'gdtoolkit-dev-env' │ ├───x86_64-darwin │ │ └───default: development environment 'gdtoolkit-dev-env' │ └───x86_64-linux │ └───default: development environment 'gdtoolkit-dev-env' └───packages ├───aarch64-darwin │ ├───default: package 'python3.13-gdtoolkit-4.3.4' │ └───gdtoolkit: package 'python3.13-gdtoolkit-4.3.4' ├───aarch64-linux │ ├───default: package 'python3.13-gdtoolkit-4.3.4' │ └───gdtoolkit: package 'python3.13-gdtoolkit-4.3.4' ├───x86_64-darwin │ ├───default: package 'python3.13-gdtoolkit-4.3.4' │ └───gdtoolkit: package 'python3.13-gdtoolkit-4.3.4' └───x86_64-linux ├───default: package 'python3.13-gdtoolkit-4.3.4' └───gdtoolkit: package 'python3.13-gdtoolkit-4.3.4'

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Really useful apps btw, thank you for all your work.