Addition of a Flake.nix for Reth

[SmolPatches]

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For those unfamiliar with the Nix Package Manager, this is a Nix based file, with various features. Within this PR I made a working Proof of Concept for Reth.

Within the file, there are two features of the flake, a build system and a portable environment.

Seamless Build

• In an isolated environment(dependencies don't interact with other system files)
• Without cloning

Examples

When inside of the reth directory

$ nix build

Without downloading the repo

$ nix build "github:smolPatches/reth?ref=feat/reth-flake"

Portable Environment

• Allows users to easily pull down the dependencies of reth in one go

Required Rust Version, Cargo Dependencies, Clang, etc.

• Seamless environment to experiment w/ building / changing reth code

Examples

When inside of the reth directory

$ nix develop

Without downloading the repo

$ nix develop "github:smolPatches/reth?ref=feat/reth-flake"

Later, I will be making a PR to Nixpkgs as well to add Reth as a Nixpkg for users to install.

NOTE: I edited the rust-version in Cargo.toml because the official Rust Version on Rust's Page is 1.81.0 and I am parsing the Cargo.toml to select the right version of Rust to use within the Flake.

      rustPlatform = pkgs.makeRustPlatform {
        rustc = pkgs.rust-bin.stable."${rustVersion}".default;
        cargo = pkgs.rust-bin.stable."${rustVersion}".default;
      };