gh-131885: Document / for codecs functions (#131992)

Author: donBarbos

Doc/library/codecs.rst

@@ -55,7 +55,7 @@ any codec:
 
 The full details for each codec can also be looked up directly:
 
-.. function:: lookup(encoding)
+.. function:: lookup(encoding, /)
 
    Looks up the codec info in the Python codec registry and returns a
    :class:`CodecInfo` object as defined below.
@@ -156,7 +156,7 @@ these additional functions which use :func:`lookup` for the codec lookup:
 Custom codecs are made available by registering a suitable codec search
 function:
 
-.. function:: register(search_function)
+.. function:: register(search_function, /)
 
    Register a codec search function. Search functions are expected to take one
    argument, being the encoding name in all lower case letters with hyphens
@@ -168,7 +168,7 @@ function:
       Hyphens and spaces are converted to underscore.
 
 
-.. function:: unregister(search_function)
+.. function:: unregister(search_function, /)
 
    Unregister a codec search function and clear the registry's cache.
    If the search function is not registered, do nothing.
@@ -416,7 +416,7 @@ In addition, the following error handler is specific to the given codecs:
 The set of allowed values can be extended by registering a new named error
 handler:
 
-.. function:: register_error(name, error_handler)
+.. function:: register_error(name, error_handler, /)
 
    Register the error handling function *error_handler* under the name *name*.
    The *error_handler* argument will be called during encoding and decoding
@@ -442,7 +442,7 @@ handler:
 Previously registered error handlers (including the standard error handlers)
 can be looked up by name:
 
-.. function:: lookup_error(name)
+.. function:: lookup_error(name, /)
 
    Return the error handler previously registered under the name *name*.