fix pattern-string in json_schema.py by removing anchors

[lapp0]

Fixes #931

Problem

interegular doesn't support anchors, ^ and $, however json_schema.py explicitly allowed their inclusion in main, resulting in interegular.patterns.Unsupported: '^'.

Solution

• Strip anchors in pattern-strings.
• update json_schema.py tests so any produced regex is run through interegular.parse_pattern(regex) to check for interegular incompatibility.