This commit introduces the `sqlc.optional` feature, allowing conditional inclusion of SQL query fragments at runtime.Key changes:1.  **Parser Enhancement**: The SQL parser now recognizes `sqlc.optional('ConditionKey', 'SQLFragment')` syntax within query files. This information is stored in the query's metadata.2.  **Code Generation**:    - Go code generation logic has been updated to process these `OptionalBlocks`.    - Generated Go functions now include new parameters (typed as `interface{}`) corresponding to each `ConditionKey`.    - Templates (`stdlib/queryCode.tmpl`, `pgx/queryCode.tmpl`) were modified to dynamically build the SQL query string and its arguments at runtime. If an optional Go parameter is non-nil, its associated SQL fragment is included in the final query, and its value is added to the list of database arguments.3.  **Parameter Handling**: `$N` placeholders in all SQL fragments (base or optional) consistently refer to the Nth parameter in the generated Go function's signature.4.  **Documentation**: Added comprehensive documentation for `sqlc.optional` in `docs/reference/query-annotations.md`, covering syntax, behavior, parameter numbering, and examples.5.  **Examples**: A new runnable example has been added to `examples/dynamic_query/postgresql/` to demonstrate practical usage.6.  **Tests**: New end-to-end tests were added in `internal/endtoend/testdata/dynamic_query/` for both `stdlib` and `pgx` drivers, ensuring the correctness of the generated code.