fix(rds): vendor mysql UDF plugin API in fakecloud_udf.c

[vieiralucas]

Summary

• Vendor minimal UDF_INIT/UDF_ARGS/Item_result definitions inline in fakecloud_udf.c, dropping the #include <mysql.h> requirement.
• Remove mysql-community-devel / libmysqlclient-dev / libmariadb-dev from both Dockerfiles — only gcc + libcurl-devel remain.
• Probe plugin dir from a known list instead of relying on mysql_config.

Why

PR #812 added mysql-community-devel to fix mysql.h: not found, but the upstream mysql:8.0 image's Dockerfile strips its community release repo after install — microdnf install mysql-community-devel returns No package matches. Re-adding the repo would hard-code a brittle Oracle URL.

The UDF plugin API surface we touch is tiny and ABI-stable across MySQL 5.6 -> 8.x and MariaDB 10.x/11.x. Vendoring is safer than depending on a repo definition Oracle removed.

Test plan

• CI RDS support images workflow builds fakecloud-mysql:8.0 on linux/amd64 and linux/arm64.
• Same for fakecloud-mariadb 10.6, 10.11, 11.4.
• Postgres images unaffected.

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Summary by cubic

Vendor minimal MySQL UDF structs inline in both mysql/fakecloud_udf.c and mariadb/fakecloud_udf.c to drop the mysql.h dependency and fix UDF builds on mysql:8.0 and MariaDB. Dockerfiles now compile the UDF with only gcc + libcurl and probe plugin directories without mysql_config.

• Bug Fixes

  • Inline UDF_INIT/UDF_ARGS/Item_result in both UDF sources and remove the include.
  • Probe common plugin dirs across OL and Debian paths (fallback to /usr/lib/mysql/plugin).
  • Build the UDF without mysql_config flags.

• Dependencies

  • Remove mysql-community-devel, libmysqlclient-dev, libmariadb-dev.
  • Keep only gcc, make, libcurl headers (libcurl-devel/libcurl4-openssl-dev), and libc headers.

^{Written for commit dd18ac9. Summary will update on new commits. Review in cubic}

[cubic-dev-ai]

No issues found across 4 files

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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