FEAT: varcharmax streaming support in execute

[gargsaumya]

Work Item / Issue Reference

AB#33395

GitHub Issue: #<ISSUE_NUMBER>

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Summary

This pull request focuses on improving type safety and error handling for parameter binding and execution in the MSSQL Python driver, especially for string and binary types. The changes ensure that only supported Python types are bound to SQL parameters and that errors are raised for unsupported types, preventing silent failures. Additionally, the data-at-execution (DAE) streaming path for strings is now more robust and explicit.

Parameter type safety and error handling:

• Changed _map_sql_type in cursor.py to raise a TypeError for unsupported parameter types instead of defaulting to SQL_VARCHAR, preventing silent type mismatches.
• In ddbc_bindings.cpp, added explicit type checks for SQL_C_CHAR and SQL_C_BINARY bindings, raising an error if the Python object is not a string or bytes-like object.

DAE (Data At Execution) streaming improvements:

• Enhanced the DAE streaming logic for SQL_C_CHAR in ddbc_bindings.cpp to handle string parameters more robustly, including chunked streaming via SQLPutData.
• Added support for chunked DAE streaming of Python str objects mapped to SQL_C_CHAR, ensuring large strings are sent in manageable pieces.

Platform-specific encoding for wide strings:

• Ensured that wide string (SQL_C_WCHAR) parameters are correctly converted to the platform-specific encoding before streaming.

[Copilot]

Pull Request Overview

This PR enhances the MSSQL Python driver by adding support for VARCHAR(MAX) streaming through data-at-execution (DAE) and improving type safety for parameter binding. The changes focus on robust handling of large string parameters and preventing silent type mismatches.

Key changes:

• Added DAE streaming support for both SQL_C_CHAR and SQL_C_WCHAR parameter types with chunked data transmission
• Enhanced type validation in parameter binding to raise explicit errors for unsupported types
• Added comprehensive test coverage for VARCHAR(MAX) and NVARCHAR(MAX) operations in both LOB and non-LOB scenarios

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
mssql_python/pybind/ddbc_bindings.cpp	Implements DAE streaming logic for string parameters and adds type validation for SQL_C_CHAR and SQL_C_BINARY bindings
tests/test_004_cursor.py	Adds test cases for VARCHAR(MAX) and NVARCHAR(MAX) insert operations covering both small and large data scenarios

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