move buffer initialization to buffer_create

Description

Move the buffer initialization to the create_buffer routines. The initialization to zero is controlled by an optional argument.

News snippet

Move the buffer initialization to the create_buffer routines.

Checklist

• I have checked that my code follows the Octopus coding standards
• I have added tests for all the new features added in this request.

src/basic/accel.F90

@@ -728,7 +728,7 @@ contains
     !%Type logical
     !%Section Execution::Accel
     !%Description
-    !% Initialize new GPU buffers to zero on creation (use only for debugging, as it has an performance impact!).
+    !% Initialize new GPU buffers to zero on creation (use only for debugging, as it has a performance impact!).
     !%End
     call parse_variable(namespace, 'ZeroGPUBuffers', .false., accel%zero_buffers)