Add FormationError and OccurrenceConstraintViolationError (#490)

In OCPP 1.6, two errors were misspelled. "FormationViolation" Error
should be "FormatViolation" Error, "OccurenceConstraintViolation" Error
should be "OccurrenceConstraintViolation" Error.

The OCA decided not to correct the spelling in OCPP 1.6, since that
would be a breaking change. FormationViolation has been fixed as of OCPP
2.0.1. OccurenceConstraintViolation Error is used for 1.6 and 2.0.1.
"OccurrenceConstraintViolation" Error is used for OCPP 2.1 and up.

This library doesn't support "FormationViolation" Error (for OCPP 1.6
and up)

This commit  adds support for those errors.

See the discussion at #381
and OCPP 1.6-J Errata sheet v1.0, section 5 "Known issues that won't be
fixed".

CHANGELOG.md

@@ -1,5 +1,8 @@
 # Change log
 
+
+- [#381](https://github.com/mobilityhouse/ocpp/issues/381) FormatViolation serialization bug with OCPP 1.6-J
+
 ## 0.21.0 (2023-10-19) 
 
 - [#492] Minor fixes _handle_call doc string  - Thanks @drc38

ocpp/exceptions.py

@@ -68,12 +68,31 @@ class SecurityError(OCPPError):
 
 
 class FormatViolationError(OCPPError):
+    """
+    Not strict OCPP 1.6 - see FormationViolationError
+    Valid OCPP 2.0.1
+    """
+
     code = "FormatViolation"
     default_description = (
         "Payload for Action is syntactically incorrect or " "structure for Action"
     )
 
 
+class FormationViolationError(OCPPError):
+    """
+    To allow for strict OCPP 1.6 compliance
+        5. Known issues that will not be fixed
+        5.2. Page 14, par 4.2.3. CallError: incorrect name in enum: FormationViolation
+        Incorrect name in enum: FormationViolation
+    """
+
+    code = "FormationViolation"
+    default_description = (
+        "Payload for Action is syntactically incorrect or structure for Action"
+    )
+
+
 class PropertyConstraintViolationError(OCPPError):
     code = "PropertyConstraintViolation"
     default_description = (
@@ -83,6 +102,14 @@ class PropertyConstraintViolationError(OCPPError):
 
 
 class OccurenceConstraintViolationError(OCPPError):
+    """
+    To allow for strict OCPP 1.6 compliance
+    ocpp-j-1.6-errata-sheet.pdf
+        5. Known issues that will not be fixed
+        5.1. Page 14, par 4.2.3: CallError: Typo in enum
+        Typo in enum: OccurenceConstraintViolation
+    """
+
     code = "OccurenceConstraintViolation"
     default_description = (
         "Payload for Action is syntactically correct but "
@@ -91,6 +118,20 @@ class OccurenceConstraintViolationError(OCPPError):
     )
 
 
+class OccurrenceConstraintViolationError(OCPPError):
+    """
+    Not strict OCPP 1.6 - see OccurenceConstraintViolationError
+    Valid OCPP 2.0.1
+    """
+
+    code = "OccurrenceConstraintViolation"
+    default_description = (
+        "Payload for Action is syntactically correct but "
+        "at least one of the fields violates occurence "
+        "constraints"
+    )
+
+
 class TypeConstraintViolationError(OCPPError):
     code = "TypeConstraintViolation"
     default_description = (