MDEV-40166 fix: Time functions, data reclaim scenarios and tests

[drrtuy]

Add MySQL-compatible time functions, storage v1.5.2, and secure run_in_duckdb()

What

Bundles several DuckDB storage-engine improvements: fills gaps in
MariaDB↔DuckDB time-function compatibility, upgrades the on-disk storage
format to unlock better compression, and hardens the run_in_duckdb() UDF.

Key changes

• Time functions (duckdb_mysql_compat.cc, duckdb_manager.cc): 2-arg WEEK/YEARWEEK ported from MariaDB week logic, plus utc_time/utc_timestamp/utc_date, unix_timestamp, time_to_sec macros.
• Storage format (duckdb_manager.cc): pin serialization_compatibility to v1.5.2 so new DBs use advanced column compression (e.g. DICT_FSST), shrinking file size.
• Security (duckdb_udf.cc, ha_duckdb.cc): run_in_duckdb() now requires SUPER privilege and the new --duckdb-allow-run-in-duckdb sysvar.
• Build: rename fiber_context.c → .cpp.
• Tests/docs: new duckdb_time_func, duckdb_time_func_unsupported, run_in_duckdb_access, space_reclaim tests + space-reclaim docs.

How to test

Run the DuckDB suite: mysql-test-run --suite=duckdb duckdb_time_func run_in_duckdb_access space_reclaim.

[gemini-code-assist]

Code Review

This pull request introduces several enhancements and compatibility fixes for the DuckDB storage engine integration. Key changes include adding access control to the run_in_duckdb() function (requiring the SUPER privilege and a new global system variable duckdb_allow_run_in_duckdb), pinning the default storage format version to v1.5.2 to leverage modern column compression, and implementing several MySQL-compatible date/time function overloads (WEEK, YEARWEEK, TO_DAYS, DAYOFWEEK, and WEEKDAY) to ensure consistent behavior during pushdown. Additionally, comprehensive documentation and tests for space reclamation and access control have been added. Feedback on the code changes highlights a potential bug in mc_calc_weekday where negative day numbers (e.g., for BC dates) can result in negative weekday values, leading to incorrect week calculations when cast to unsigned integers.

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