fix(spanner): restore implicit database_dialect reload in sync client (#1537)

**Problem**
Following the introduction of AsyncIO support via CrossSync, code
generation for the synchronous client caused a regression in
Database.database_dialect.

Previously, if the property was accessed and returned
DATABASE_DIALECT_UNSPECIFIED, the client would implicitly make a
blocking self.reload() to retrieve the dialect from the server. This was
lost during the shift to CrossSync as properties cannot be asynchronous
in the _async source of truth.

**Solution**
Restore the lazy-loading reload behavior via an environment check:

__async/database.py_: Added if not CrossSync.is_async: guard directly
into the database_dialect getter. This makes it un-reachable code in the
async runtime (where blocking properties or un-awaited coroutines are
frowned upon).
_database.py_: The generator strips the CrossSync context into a
standard synchronous self.reload() call, successfully maintaining strict
backwards compatibility for all existing synchronous libraries.

Author: sinhasubham

packages/google-cloud-spanner/google/cloud/spanner_v1/_async/database.py

@@ -410,6 +410,9 @@ def database_dialect(self):
         :rtype: :class:`google.cloud.spanner_admin_database_v1.types.DatabaseDialect`
         :returns: the dialect of the database
         """
+        if self._database_dialect == DatabaseDialect.DATABASE_DIALECT_UNSPECIFIED:
+            if not CrossSync.is_async:
+                self.reload()
         return self._database_dialect
 
     @property

packages/google-cloud-spanner/google/cloud/spanner_v1/database.py

@@ -358,6 +358,8 @@ def database_dialect(self):
 
         :rtype: :class:`google.cloud.spanner_admin_database_v1.types.DatabaseDialect`
         :returns: the dialect of the database"""
+        if self._database_dialect == DatabaseDialect.DATABASE_DIALECT_UNSPECIFIED:
+            self.reload()
         return self._database_dialect
 
     @property