Changelog category (leave one):

• Backward Incompatible Change

Changelog entry (a user-readable short description of the changes that goes to CHANGELOG.md):

Merge tables will unify the structure of underlying tables by using a union of their columns and deriving common types. This closes #64864. This closes #35307. In certain cases, this change could be backward incompatible. One example is when there is no common type between tables, but conversion to the type of the first table is still possible, such as in the case of UInt64 and Int64 or any numeric type and String. If you want to return to the old behavior, set merge_table_max_tables_to_look_for_schema_inference to 1 or set compatibility to 24.12 or earlier.

Information about CI checks: https://clickhouse.com/docs/en/development/continuous-integration/

CI Settings (Only check the boxes if you know what you are doing)

All builds in Builds_1 and Builds_2 stages are always mandatory
and will run independently of the checks below:

• Allow: All Required Checks
• Allow: Stateless tests
• Allow: Stateful tests
• Allow: Integration Tests
• Allow: Performance tests
• Allow: All Builds
• Allow: batch 1, 2 for multi-batch jobs
• Allow: batch 3, 4, 5, 6 for multi-batch jobs

• Exclude: Style check
• Exclude: Fast test
• Exclude: All with ASAN
• Exclude: All with TSAN, MSAN, UBSAN, Coverage
• Exclude: All with aarch64
• Exclude: All with release
• Exclude: All with debug

• Run only fuzzers related jobs (libFuzzer fuzzers, AST fuzzers, etc.)
• Exclude: AST fuzzers

• Do not test
• Woolen Wolfdog
• Upload binaries for special builds
• Disable merge-commit
• Disable CI cache