FIX: Execute returning cursor object (#161)

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> AB#3806

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### Summary   
This pull request enhances the `Cursor` class in
`mssql_python/cursor.py` to support method chaining by modifying the
`execute` method to return the cursor itself. It also introduces
comprehensive test coverage for method chaining in
`tests/test_004_cursor.py`.

### Enhancements to the `Cursor` class:
* Modified the `execute` method in `mssql_python/cursor.py` to return
the `Cursor` instance, enabling method chaining. (`[[1]]

### Updates to test cases:
* Simplified the `test_longwvarchar` test by removing unnecessary loops
and assertions, improving readability.
* Added new test cases to validate method chaining functionality,
including:
- Chaining `execute` with `fetchone`, `fetchall`, `fetchmany`,
`rowcount`, and `description`.
  - Testing multiple sequential operations and parameterized queries. 
- Ensuring chaining works correctly after errors and with statement
reuse for performance.

---------

Co-authored-by: Jahnvi Thakkar <jathakkar@microsoft.com>

Author: jahnvi480

mssql_python/constants.py

@@ -97,7 +97,6 @@ class ConstantsDDBC(Enum):
     SQL_ATTR_ROW_ARRAY_SIZE = 27
     SQL_ATTR_ROWS_FETCHED_PTR = 26
     SQL_ATTR_ROW_STATUS_PTR = 25
-    SQL_FETCH_NEXT = 1
     SQL_ROW_SUCCESS = 0
     SQL_ROW_SUCCESS_WITH_INFO = 1
     SQL_ROW_NOROW = 100
@@ -117,6 +116,14 @@ class ConstantsDDBC(Enum):
     SQL_NULLABLE = 1
     SQL_MAX_NUMERIC_LEN = 16
 
+    SQL_FETCH_NEXT = 1
+    SQL_FETCH_FIRST = 2
+    SQL_FETCH_LAST = 3
+    SQL_FETCH_PRIOR = 4
+    SQL_FETCH_ABSOLUTE = 5
+    SQL_FETCH_RELATIVE = 6
+    SQL_FETCH_BOOKMARK = 8
+
 class AuthType(Enum):
     """Constants for authentication types"""
     INTERACTIVE = "activedirectoryinteractive"