feat: add pet-hatch locator for Hatch environments (Fixes #450) (#460)

Fixes #450.

Adds a new `pet-hatch` crate so Hatch-managed virtual environments are
no longer misclassified as plain `Venv` by downstream consumers.

### Implementation

Matches Hatch's actual storage layout from
[`src/hatch/env/virtual.py`](https://github.com/pypa/hatch/blob/master/src/hatch/env/virtual.py):

- **Default storage:**
`<data_dir>/env/virtual/<project_name>/<project_id>/<venv_name>` (3
levels deep, not 2).
- **`HATCH_DATA_DIR`** is honoured and never silently falls back to the
platform default when set.
- **Project-local discovery** via `[tool.hatch.dirs.env].virtual` in
`pyproject.toml` or `[dirs.env]` in `hatch.toml`. Handles the `virtual =
".hatch"` example called out in the issue.
- Hatch locator is inserted **before `Venv`** so it claims envs first.
- `LocatorKind::Hatch` registered as
`RefreshStatePersistence::ConfiguredOnly` (workspace-driven discovery).

### Tests

15 unit tests covering:
- Default-storage layout matches at exactly 3 levels deep; rejects
2-deep and 4-deep prefixes.
- `HATCH_DATA_DIR` semantics — used when set, no fallback to platform
default.
- Project-local discovery via both `pyproject.toml` and `hatch.toml`;
rejected without `dirs.env.virtual` config.
- Per-platform `platformdirs` defaults (Linux/macOS/Windows).

### Replaces #451

This PR replaces #451, which had a fundamental layout bug: it assumed
envs are stored 2 levels deep under `<data_dir>/env/virtual`
(`<project-hash>/<env-name>`). Per Hatch's source, the actual layout is
3 levels deep (`<project_name>/<project_id>/<venv_name>`), so #451 would
fail to detect any real Hatch env in the default storage location.

Author: karthiknadig

Cargo.lock

@@ -43,6 +43,7 @@ pub struct Configuration {
 #[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord)]
 pub enum LocatorKind {
     Conda,
+    Hatch,
     Homebrew,
     LinuxGlobal,
     MacCommandLineTools,

crates/pet-core/src/lib.rs

@@ -19,6 +19,7 @@ pub enum PythonEnvironmentKind {
     PyenvVirtualEnv, // Pyenv virtualenvs.
     Pipenv,
     Poetry,
+    Hatch,
     MacPythonOrg,
     MacCommandLineTools,
     LinuxGlobal,

crates/pet-core/src/python_environment.rs

@@ -0,0 +1,16 @@
+[package]
+name = "pet-hatch"
+version.workspace = true
+edition.workspace = true
+license.workspace = true
+
+[dependencies]
+pet-core = { path = "../pet-core" }
+pet-fs = { path = "../pet-fs" }
+pet-python-utils = { path = "../pet-python-utils" }
+serde = { version = "1.0.152", features = ["derive"] }
+toml = "0.9.7"
+log = "0.4.21"
+
+[dev-dependencies]
+tempfile = "3.13"