Implement CONTEXT_INFO and SESSION_CONTEXT features

[celsowm]

I have implemented a set of features related to session state management, bringing Iridium SQL closer to 1:1 compatibility with SQL Server. Specifically, I added support for CONTEXT_INFO and SESSION_CONTEXT.

Features Implemented:

1. SET CONTEXT_INFO Statement: Users can now set a 128-byte binary context for their session using literals (e.g., SET CONTEXT_INFO 0xABCD) or variables.
2. CONTEXT_INFO() Function: A new scalar function to retrieve the current session's context info.
3. SESSION_CONTEXT Key-Value Store: Implemented the SQL Server 2016+ session context feature.
   • sp_set_session_context: A system stored procedure to set key-value pairs, with support for the @read_only flag.
   • SESSION_CONTEXT(key): A scalar function to retrieve values by key.
4. sys.dm_exec_sessions Integration: Added the context_info column to this DMV, enabling introspection of session context.
5. Robustness: The session state is properly integrated into the engine's snapshotting mechanism, ensuring consistency across savepoints and transaction rollbacks.

Verification:

• Added a new integration test file crates/iridium_core/tests/session_context_test.rs covering all new features and edge cases (e.g., read-only context keys).
• Ran the full iridium_core test suite (~1300+ tests) to ensure no regressions were introduced.
• The implementation follows the existing architectural patterns for parsing, AST lowering, and execution.

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PR created automatically by Jules for task 7295642607711709711 started by @celsowm

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