Operations.add_column

This release enhances the `merge` command with `--splice` support and improves head revision detection logic. It also fixes several bugs related to autogenerated script rendering and dialect comparisons for MySQL ENUMs.

This patch reverts the automatic inline rendering of PRIMARY KEY constraints in `Operations.add_column()` introduced in 1.18.2, making this behavior explicitly opt-in via the new `inline_primary_key` parameter.

This release enhances `Operations.add_column()` by honoring the `primary_key` parameter and introducing the `inline_references` option for foreign key rendering. A typing bug affecting server default parameters in `AlterColumnOp` was also resolved.