refactor: Remove boolean_true_literal, use TRUE for both backends

MySQL accepts TRUE as a boolean literal (alias for 1), so we can
use TRUE universally instead of having backend-specific literals.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: dimitri-yatsenko

src/datajoint/adapters/base.py

@@ -563,21 +563,6 @@ def supports_inline_indexes(self) -> bool:
         """
         return True  # Default for MySQL, override in PostgreSQL
 
-    @property
-    def boolean_true_literal(self) -> str:
-        """
-        Return the SQL literal for boolean TRUE.
-
-        MySQL uses 1 (since bool maps to tinyint).
-        PostgreSQL uses TRUE (native boolean type).
-
-        Returns
-        -------
-        str
-            SQL literal for boolean true value.
-        """
-        return "1"  # Default for MySQL, override in PostgreSQL
-
     def create_index_ddl(
         self,
         full_table_name: str,

src/datajoint/adapters/postgres.py

@@ -710,20 +710,6 @@ def supports_inline_indexes(self) -> bool:
         """
         return False
 
-    @property
-    def boolean_true_literal(self) -> str:
-        """
-        Return the SQL literal for boolean TRUE.
-
-        PostgreSQL uses native boolean type with TRUE literal.
-
-        Returns
-        -------
-        str
-            SQL literal for boolean true value.
-        """
-        return "TRUE"
-
     # =========================================================================
     # Introspection
     # =========================================================================

src/datajoint/declare.py

@@ -477,12 +477,11 @@ def declare(
         primary_key = ["_singleton"]
         singleton_comment = ":bool:singleton primary key"
         sql_type = adapter.core_type_to_sql("bool")
-        bool_literal = adapter.boolean_true_literal
         singleton_sql = adapter.format_column_definition(
             name="_singleton",
             sql_type=sql_type,
             nullable=False,
-            default=f"NOT NULL DEFAULT {bool_literal}",
+            default="NOT NULL DEFAULT TRUE",
             comment=singleton_comment,
         )
         attribute_sql.insert(0, singleton_sql)