feat(csv-loader): add support for custom type declarations

Introduce the ability to define reusable types within CSV files using
comment lines with the format `# TypeName := schema`.

- Support parsing type declarations from comments or schema cells
- Enable recursive expansion of type names within schemas
- Integrate declared types into generated TypeScript definitions
- Allow columns to reference declared types by name

src/csv-loader/type-gen.ts

@@ -1,6 +1,6 @@
 import * as path from "path";
 import { schemaToTypeString } from "../index.js";
-import type { PropertyConfig } from "./types.js";
+import type { PropertyConfig, TypeDeclaration } from "./types.js";
 
 /**
  * Generate TypeScript interface for the CSV data
@@ -10,6 +10,7 @@ export function generateTypeDefinition(
   propertyConfigs: PropertyConfig[],
   references: Set<string>,
   currentFilePath?: string,
+  typeDeclarations: TypeDeclaration[] = [],
 ): string {
   const typeName = resourceName ? `${resourceName}Table` : "Table";
   const currentTableName = currentFilePath
@@ -44,11 +45,24 @@ export function generateTypeDefinition(
 
   const importSection = imports.length > 0 ? imports.join("\n") + "\n\n" : "";
 
+  // Generate type declarations for user-defined types
+  const typeDeclarationSection =
+    typeDeclarations.length > 0
+      ? typeDeclarations
+          .map(
+            (decl) =>
+              `type ${decl.name} = ${schemaToTypeString(decl.schema, resourceNames)};`,
+          )
+          .join("\n") + "\n\n"
+      : "";
+
   const properties = propertyConfigs
-    .map(
-      (config) =>
-        `    readonly ${config.name}: ${schemaToTypeString(config.schema, resourceNames)};`,
-    )
+    .map((config) => {
+      const typeStr = config.declaredTypeName
+        ? config.declaredTypeName
+        : schemaToTypeString(config.schema, resourceNames);
+      return `    readonly ${config.name}: ${typeStr};`;
+    })
     .join("\n");
 
   let exportAlias = "";
@@ -58,7 +72,7 @@ export function generateTypeDefinition(
     exportAlias = `\nexport type ${singularType} = ${typeName}[number];`;
   }
 
-  return `${importSection}type ${typeName} = readonly {
+  return `${importSection}${typeDeclarationSection}type ${typeName} = readonly {
 ${properties}
 }[];
 ${exportAlias}