chore: add nix flake setup (#270)

Author: sunng87

.gitignore

@@ -3,4 +3,6 @@
 tests-integration/test-server/target
 tests-integration/rust-client/target
 node_modules
-.DS_Store
+.DS_Store
+.direnv
+.envrc

flake.lock

@@ -0,0 +1,61 @@
+{
+  description = "Development environment flake";
+
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixos-25.05";
+    fenix = {
+      url = "github:nix-community/fenix";
+      inputs.nixpkgs.follows = "nixpkgs";
+    };
+    flake-utils.url = "github:numtide/flake-utils";
+  };
+
+  outputs = { self, nixpkgs, fenix, flake-utils }:
+    flake-utils.lib.eachDefaultSystem (system:
+      let
+        pkgs = nixpkgs.legacyPackages.${system};
+        pythonEnv = pkgs.python3.withPackages (ps: with ps; [
+          psycopg
+        ]);
+        buildInputs = with pkgs; [
+          llvmPackages.libclang
+          duckdb.dev
+          duckdb.lib
+          sqlite.dev
+        ];
+      in
+      {
+        devShells.default = pkgs.mkShell {
+          nativeBuildInputs = with pkgs; [
+            pkg-config
+            clang
+            git
+            mold
+            (fenix.packages.${system}.stable.withComponents [
+              "cargo"
+              "clippy"
+              "rust-src"
+              "rustc"
+              "rustfmt"
+              "rust-analyzer"
+            ])
+            cargo-nextest
+            cargo-release
+            curl
+            gnuplot ## for cargo bench
+            pythonEnv
+            postgresql
+          ];
+
+          LD_LIBRARY_PATH = pkgs.lib.makeLibraryPath buildInputs;
+          shellHook = ''
+            export CC=clang
+            export CXX=clang++
+            export SQLITE3_LIB_DIR="${pkgs.sqlite.dev}/lib"
+            export SQLITE3_INCLUDE_DIR="${pkgs.sqlite.dev}/include"
+            export DUCKDB_LIB_DIR="${pkgs.duckdb.lib}/lib"
+            export DUCKDB_INCLUDE_DIR="${pkgs.duckdb.dev}/include"
+          '';
+        };
+      });
+}