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[AB#39058](https://sqlclientdrivers.visualstudio.com/c6d89619-62de-46a0-8b46-70b92a84d85e/_workitems/edit/39058)

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### Summary   
This pull request introduces comprehensive support for setting ODBC
connection attributes in the `mssql_python` library, aligning its
functionality with pyodbc's `set_attr` API. The changes include new
constants for connection attributes, transaction isolation levels, and
related options, as well as robust error handling and input validation
in both Python and C++ layers. This enables users to configure
connection behavior (e.g., autocommit, isolation level, timeouts) in a
standardized and secure manner.

### Connection Attribute Support

* Added a wide set of ODBC connection attribute constants, transaction
isolation level constants, access mode constants, and related enums to
`mssql_python/__init__.py` and `mssql_python/constants.py`, making them
available for use in Python code.
* Implemented the `set_attr` method in the `Connection` Python class,
providing pyodbc-compatible functionality for setting connection
attributes with detailed input validation and error handling.

### C++ Backend Enhancements

* Exposed `setAttribute` as a public method in the C++ `Connection`
class, and added a new `setAttr` method in `ConnectionHandle`, with
improved error reporting and range validation for SQLUINTEGER values.
* Registered the new `set_attr` method with the Python bindings, making
it accessible from Python code.

### Code Cleanup and Refactoring

* Moved and consolidated connection attribute constants in
`ConstantsDDBC` to improve maintainability, and removed legacy/unused
constants.

These changes provide a robust interface for configuring ODBC connection
attributes, improve compatibility with pyodbc, and enhance error
handling for attribute operations.