Avoid rebuilds

[srid]

resolves #12

• nix run is cached
• nix flake check (clippy) is cached

[srid]

While this does work, it breaks the cargo-leptos generated wasm binary. server fns, and signals are broken. logging doesn't work as well. But route switches work.

[srid]

This approach suffers from another problem. It is not gonna work with projects using cargo workspaces, because the dummy source obviously doesn't include them, yet Cargo.toml can refer to the local crates (such as leptos_extra from https://github.com/juspay/nix-browser)

Ref:

       >
       > Caused by:
       >     `cargo metadata` exited with an error: error: failed to load manifest for dependency `leptos_extra`
       >
       >     Caused by:
       >       failed to read `/private/tmp/nix-build-nix-browser-deps-0.1.0.drv-1/dummy-src/crates/leptos_extra/Cargo.toml`