♻️🍱💩👷 crates/vanth, project: Refactor entity system and setup; migrate to Nix flakes

- Add `.cargo/config.toml` with target directory and rustflags configuration.
- Remove devenv files and set up Nix flake configuration with `flake.nix` and `flake.lock`.
- Add dependencies on `blake3`, `digest`, and hashing-related crates for content hashing functionality.
- Implement `EntityId` as hashed representation and `ContentHash` component using Blake3.
- Add `hashing_serializer` module for serializing and hashing components.
- Remove unused `parser` module and restructure lib.rs with new `Reference` type and storage interfaces.
- Add test files for `store` and `reference` functionality with TODOs for implementation.
- Introduce `VanthPlugin` skeleton and entity save/load interfaces with placeholder implementations.
- Add `Reference` type with retrieval state machine and async handling stubs.

flake.lock

@@ -0,0 +1,130 @@
+{
+  "nodes": {
+    "crane": {
+      "locked": {
+        "lastModified": 1754112045,
+        "narHash": "sha256-ZgsUm1brDXTPSLK5kY5rkQkqqr2oM1Pd20oirH3Sgkk=",
+        "owner": "ipetkov",
+        "repo": "crane",
+        "rev": "b91f27c93d9d414a21092d85ed5ac9def8624b91",
+        "type": "github"
+      },
+      "original": {
+        "owner": "ipetkov",
+        "repo": "crane",
+        "type": "github"
+      }
+    },
+    "fenix": {
+      "inputs": {
+        "nixpkgs": "nixpkgs",
+        "rust-analyzer-src": "rust-analyzer-src"
+      },
+      "locked": {
+        "lastModified": 1754116698,
+        "narHash": "sha256-2cMDogXcqv975o191g0/6ZM0UolJ2X0ChuuLaNKbNAM=",
+        "owner": "nix-community",
+        "repo": "fenix",
+        "rev": "acdb7d8af407ea8aee21b028dc58b4bc51a7849a",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nix-community",
+        "repo": "fenix",
+        "type": "github"
+      }
+    },
+    "flake-parts": {
+      "inputs": {
+        "nixpkgs-lib": "nixpkgs-lib"
+      },
+      "locked": {
+        "lastModified": 1754091436,
+        "narHash": "sha256-XKqDMN1/Qj1DKivQvscI4vmHfDfvYR2pfuFOJiCeewM=",
+        "owner": "hercules-ci",
+        "repo": "flake-parts",
+        "rev": "67df8c627c2c39c41dbec76a1f201929929ab0bd",
+        "type": "github"
+      },
+      "original": {
+        "owner": "hercules-ci",
+        "repo": "flake-parts",
+        "type": "github"
+      }
+    },
+    "nixpkgs": {
+      "locked": {
+        "lastModified": 1753939845,
+        "narHash": "sha256-K2ViRJfdVGE8tpJejs8Qpvvejks1+A4GQej/lBk5y7I=",
+        "owner": "nixos",
+        "repo": "nixpkgs",
+        "rev": "94def634a20494ee057c76998843c015909d6311",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nixos",
+        "ref": "nixos-unstable",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "nixpkgs-lib": {
+      "locked": {
+        "lastModified": 1753579242,
+        "narHash": "sha256-zvaMGVn14/Zz8hnp4VWT9xVnhc8vuL3TStRqwk22biA=",
+        "owner": "nix-community",
+        "repo": "nixpkgs.lib",
+        "rev": "0f36c44e01a6129be94e3ade315a5883f0228a6e",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nix-community",
+        "repo": "nixpkgs.lib",
+        "type": "github"
+      }
+    },
+    "nixpkgs_2": {
+      "locked": {
+        "lastModified": 1754060105,
+        "narHash": "sha256-di5L6e5Iiv+oegS07j9h23FdqEpXn0ZQqMlDOEMw1EY=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "e7eabdc701d7dbb810fd91a97ec358caa4c1fc50",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "ref": "nixpkgs-unstable",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "root": {
+      "inputs": {
+        "crane": "crane",
+        "fenix": "fenix",
+        "flake-parts": "flake-parts",
+        "nixpkgs": "nixpkgs_2"
+      }
+    },
+    "rust-analyzer-src": {
+      "flake": false,
+      "locked": {
+        "lastModified": 1753974682,
+        "narHash": "sha256-Ya4Ecj8JaKkapgYCCybzZBcypXpblhuG0hVDzdy2zyo=",
+        "owner": "rust-lang",
+        "repo": "rust-analyzer",
+        "rev": "68e7ec90bf29c9b17d0dcdb3358de5dee7f4afb5",
+        "type": "github"
+      },
+      "original": {
+        "owner": "rust-lang",
+        "ref": "nightly",
+        "repo": "rust-analyzer",
+        "type": "github"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}