feat(nix): add comprehensive Nix flake for linux-rust

[doprz]

Features:

• Nix Flake Configuration: Complete flake setup supporting multiple architectures
  • crane
  • flake-parts
  • flake-compat
  • treefmt-nix
    • nixfmt-rfc-style
• Development Shell: Pre-configured dev environment
• Multiple Entry Points: Support for nix develop, nix run, and nix build

[doprz]

Notes:

• Merging this into Add new linux app #241
• This PR works however as of e2d17b8, linux-rust errors:

thread '<unnamed>' (1319932) panicked at src/main.rs:67:63:
ERROR librepods::ui::window] UI message channel closed

This means that while cargo will continue to print to stderr, the nix run command will exit due to this.

[doprz]

Also went ahead and fixed some lint and formatting warnings/errors to clean up this PR.
No need to squash commits for this PR to keep nix and rust-specific changes separate.

[kavishdevar]

btw, the UI message channel closed might be because the deserialization of saved devices failing, try removing the ~/.local/share/librepods folder.

[kavishdevar]

oh TIL rebase and merge adds me as the author

[doprz]

oh TIL rebase and merge adds me as the author

It keeps me as the author but adds you as the committer.

Thank you for merging the PR! Looking forwards to future changes and development on librepods!