Lots more Document data definition

Schedule updates:

* Defined Schedule types
* Updated schedule loader to validate with pydantic
* Added ability to specify predecessor type and lead/lag

Other structural/outline stuff as well

Oh and added a unit test.

tests/unit/models/test_document_model.py

@@ -0,0 +1,53 @@
+"""Tests for Document model."""
+
+from datetime import datetime
+
+import pytest
+from pydantic import ValidationError
+
+from nrsk.models import Document
+
+
+@pytest.fixture
+def valid_document_data():  # noqa: D103
+    return {
+        "uuid": "2deac04a-d1d1-4e42-b1a7-cc941d9da9b5",
+        "title": "Project Proposal Q4",
+        "revision": "2",
+        "type": "CALC",
+        "originators": ["jane@example.com"],
+        "review_status": "IN REVIEW",
+        "status": "RESERVED",
+    }
+
+
+def test_document_model_success(valid_document_data):
+    """Test that valid input data correctly creates a Document instance."""
+    doc = Document(**valid_document_data)
+
+    assert isinstance(doc, Document)
+    assert doc.title == "Project Proposal Q4"
+    assert doc.status == Document.STATUS.RESERVED
+    assert doc.status.value == "RESERVED"
+    assert doc.status_category == "Not Yet Approved"
+
+
+@pytest.mark.parametrize(
+    "invalid_status",
+    [
+        "Reserved",  # Capitalized (case sensitive)
+        "re-served",  # Hyphenated (typo)
+        "finalized",  # Non-existent status
+        123,  # Wrong type (integer)
+    ],
+)
+def test_document_status_invalid_enum(valid_document_data, invalid_status):
+    """Tests that the model raises ValidationError for invalid status strings."""
+    data = valid_document_data.copy()
+    data["status"] = invalid_status
+
+    with pytest.raises(ValidationError) as excinfo:
+        Document(**data)
+
+    assert any("status" in err["loc"] for err in excinfo.value.errors())
+    assert "Input should be " in str(excinfo.value)