Add missing SessionContext deregister methods

[timsaucer]

Summary

Upstream DataFusion provides methods to deregister user-defined functions, but only deregister_table is exposed in datafusion-python. The UDF deregister methods are needed for dynamic function management.

Missing Methods

• deregister_udf — unregister a user-defined scalar function
• deregister_udaf — unregister a user-defined aggregate function
• deregister_udwf — unregister a user-defined window function
• deregister_udtf — unregister a user-defined table function
• deregister_object_store — unregister an object store

Upstream Reference

• https://docs.rs/datafusion/53.0.0/datafusion/execution/context/struct.SessionContext.html

Implementation

• Rust bindings: crates/core/src/context.rs
• Python wrappers: python/datafusion/context.py

Note: This gap analysis was performed using an AI agent comparing upstream DataFusion v53 documentation against the current datafusion-python codebase.