Add LOB support

[Vnajeb]

Resolves #88

Changes proposed in this pull request:

• LOB columns previously came back as raw, unwrapped values. CLOB, NCLOB, DBCLOB, and BLOB column values are now wrapped in new ClobValue/BlobValue objects in lob.py that expose a PEP 249-style read() method, matching DB-API 2.0.
• Wrapping now happens automatically for every row. row_to_tuple inspects each column's SQL type and wraps LOB values on the way out, so callers get ClobValue/BlobValue instances without any extra opt-in.
• Terse-mode rows were silently missing this wrapping. cursor.execute(sql, isTerseResults=True) used to return raw CLOB/BLOB values in list rows since the old code only handled dicts it now wraps list rows the same way, so both row shapes behave consistently.
• Backed by 56 new/updated unit tests. tests/unit/test_lob.py covers ClobValue/BlobValue construction, read() chunking/exhaustion, and NULL handling, while tests/unit/test_cursor_pep249.py adds end-to-end coverage through Cursor.execute/fetchone/fetchall, including the terse-mode regression case.