feat: add column update_on for user functions table

[KKould]

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Summary

• fixes: Feat: support update_on field for udf #14558

Tests

• Unit Test
• Logic Test
• Benchmark Test
• No Test - Explain why

Type of change

• Bug Fix (non-breaking change which fixes an issue)
• New Feature (non-breaking change which adds functionality)
• Breaking Change (fix or feature that could cause existing functionality not to work as expected)
• Documentation Update
• Refactoring
• Performance Improvement
• Other (please describe):

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This change is 

[drmingdrmer]

@drmingdrmer reviewed 16 of 21 files at r1.
Reviewable status: 16 of 21 files reviewed, all discussions resolved

[KKould]

@codex review

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[Copilot]

Pull request overview

This PR adds an update_on timestamp field to the user functions table to track when a UDF was last modified, addressing issue #14558. The field is added alongside the existing created_on timestamp.

• Adds update_on field to the UserDefinedFunction struct and protobuf schema
• Updates all UDF creation paths to initialize both created_on and update_on timestamps
• Modifies the system table schema and queries to include the new column

Reviewed changes

Copilot reviewed 21 out of 21 changed files in this pull request and generated 10 comments.

Show a summary per file

File	Description
src/meta/protos/proto/udf.proto	Adds optional update_on field (field 11) to UserDefinedFunction protobuf message
src/meta/proto-conv/src/udf_from_to_protobuf_impl.rs	Implements serialization/deserialization for update_on field, defaulting to created_on when absent for backward compatibility
src/meta/proto-conv/src/util.rs	Documents the schema change as version 160 in the metadata changelog
src/meta/proto-conv/tests/it/*.rs	Updates existing tests to include update_on field, setting it equal to created_on for backward compatibility tests
src/meta/proto-conv/tests/it/v160_udf_update_on.rs	Adds new test specifically for the update_on field with different timestamps for created and updated times
src/meta/proto-conv/tests/it/main.rs	Registers the new v160 test module
src/meta/app/src/principal/user_defined_function.rs	Adds update_on field to struct and updates helper functions to set both timestamps
src/query/sql/src/planner/binder/udf.rs	Sets both created_on and update_on to current time when binding UDF definitions
src/query/sql/src/planner/binder/show.rs	Updates SHOW USER FUNCTIONS query to include the new update_on column
src/query/storages/system/src/user_functions_table.rs	Adds update_on column to the system table schema and populates it from UDF metadata
src/query/service/tests/it/storages/testdata/columns_table.txt	Updates test snapshot to include the new column in system.user_functions table
tests/suites/0_stateless/20+_others/20_0016_udf_timestamp.result	Updates test results to show the new update_on column in query output

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