refactor(tests): use omniread public API instead of internal module imports

- Replace deep imports with top-level omniread exports in tests
- Ensure tests validate only the supported public API surface
- Align HTML and PDF tests with documented library usage

tests/test_html_table.py

@@ -2,8 +2,13 @@ from typing import Optional
 
 from pydantic import BaseModel
 
-from omniread.html.parser import HTMLParser
-from omniread.core.content import Content
+from omniread import (
+    # core
+    Content,
+
+    # html
+    HTMLParser,
+)
 
 
 class ParsedTableHTML(BaseModel):