Fix useful typo

code_examples/1_basics/2_first_programs.py

@@ -96,7 +96,7 @@ async def _(AnswerWithThinking, Query, synalinks):
         inputs=_x0,
         outputs=_x1,
         name="chain_of_thought",
-        description="Usefull to answer in a step by step manner.",
+        description="Useful to answer in a step by step manner.",
     )
     return language_model, program
 
@@ -104,7 +104,7 @@ async def _(AnswerWithThinking, Query, synalinks):
 @app.cell
 def _(program):
     # You can print a summary of your program in a table format
-    # which is really usefull to have a quick overview of your application
+    # which is really useful to have a quick overview of your application
 
     program.summary()
     return
@@ -143,7 +143,7 @@ def _(mo):
 def _(AnswerWithThinking, language_model, synalinks):
     
     class ChainOfThought(synalinks.Program):
-        """Usefull to answer in a step by step manner.
+        """Useful to answer in a step by step manner.
 
         The first line of the docstring is provided as description for the program
         if not provided in the `super().__init__()`. In a similar way the name is
@@ -220,7 +220,7 @@ def _(ChainOfThought, Query, language_model, synalinks):
             ChainOfThought(language_model=language_model),
         ],
         name="chain_of_thought",
-        description="Usefull to answer in a step by step manner.",
+        description="Useful to answer in a step by step manner.",
     )
     program_2.summary()
     return (program_2,)

code_examples/1_basics/5_rewards_metrics_and_optimizers.py

@@ -134,7 +134,7 @@ async def _(synalinks):
         inputs=_x0,
         outputs=_x1,
         name="chain_of_thought",
-        description="Usefull to answer in a step by step manner.",
+        description="Useful to answer in a step by step manner.",
     )
 
     program.compile(

code_examples/1_basics/6_training_programs.py

@@ -85,7 +85,7 @@ async def _(gsm8k_input_data_model, gsm8k_output_data_model, synalinks):
         inputs=_x0,
         outputs=_x1,
         name="chain_of_thought",
-        description="Usefull to answer in a step by step manner.",
+        description="Useful to answer in a step by step manner.",
     )
     return language_model, program
 
@@ -135,7 +135,7 @@ def _(mo):
             larger batch will take longer to process and still result in only one update.
         - **Epochs**: A epochs is an arbitrarly cutoff, generally defined as "one pass
             over the entire dataset", used to separate training into distinct phases,
-            which is usefull for logging and periodic evaluation. When using 
+            which is useful for logging and periodic evaluation. When using 
             `validation_split` or `validation_data` with the `fit` method of Synalinks
             programs, evaluation will be run at the end of every epoch.
         """

code_examples/2_advanced/1_implementing_custom_modules_and_programs_via_subclassing.py

@@ -244,7 +244,7 @@ def _(mo):
 
         To add a variable to the module, you have to use the `add_variables` function,
         this function can only be used in the `__init__()` or in the `build()` function.
-        The build function is usefull to create variables, or initialize your module/program 
+        The build function is useful to create variables, or initialize your module/program 
         based on the actual inputs, that is not known at this stage, remember the module can
         accept any inputs.