Fix dynamic imports in SQLAlchemy dialect components

Remove runtime imports that violate PyAthena development guidelines:
- Move ExecutionContext import to top-level in base.py
- Move AthenaDDLIdentifierPreparer import to top-level in compiler.py
- Remove unnecessary comments from do_execute method

This change improves static analysis, code completion, and dependency
tracking while maintaining full functionality.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: laughingman7743

pyathena/sqlalchemy/base.py

@@ -22,6 +22,7 @@
 from sqlalchemy import exc, schema, text, types, util
 from sqlalchemy.engine import Engine, reflection
 from sqlalchemy.engine.default import DefaultDialect
+from sqlalchemy.engine.interfaces import ExecutionContext
 from sqlalchemy.sql.compiler import (
     DDLCompiler,
     GenericTypeCompiler,
@@ -378,17 +379,12 @@ def get_indexes(
         return []  # pragma: no cover
 
     def do_execute(self, cursor, statement, parameters, context=None):
-        """Execute a statement with support for execution_options."""
-        from sqlalchemy.engine.interfaces import ExecutionContext
-
-        # Check for on_start_query_execution in execution_options
         on_start_query_execution = None
         if isinstance(context, ExecutionContext):
             execution_options = context.execution_options
             if execution_options is not None:
                 on_start_query_execution = execution_options.get("on_start_query_execution")
 
-        # Execute with callback if specified
         if on_start_query_execution is not None:
             cursor.execute(statement, parameters, on_start_query_execution=on_start_query_execution)
         else:

pyathena/sqlalchemy/compiler.py

@@ -18,6 +18,7 @@
     AthenaPartitionTransform,
     AthenaRowFormatSerde,
 )
+from pyathena.sqlalchemy.preparer import AthenaDDLIdentifierPreparer
 from pyathena.sqlalchemy.types import AthenaArray, AthenaMap, AthenaStruct
 
 if TYPE_CHECKING:
@@ -271,8 +272,6 @@ def __init__(
         render_schema_translate: bool = False,
         compile_kwargs: Optional[Dict[str, Any]] = None,
     ):
-        from pyathena.sqlalchemy.preparer import AthenaDDLIdentifierPreparer
-
         self._preparer = AthenaDDLIdentifierPreparer(dialect)
         super().__init__(
             dialect=dialect,