Disable non-standard functions in strict mode

[jg-rp]

This PR changes JSONPathEnvironment.setup_function_extensions() to skip registering non-standard functions when strict is True.

Standard functions are those defined by RFC 9535, count, length, match, search and value.

Non-standard, built-in function are:

• isinstance (alias is)
• typeof (alias type)
• startswith
• keys

[He-Pin]

Not sure if this is right, the rfc says we can register methods.

[jg-rp]

Yeah, there's nothing stopping users registering non-standard functions with their own JSONPathEnvironment subclass. It's just that I'm offering two preconfigured environments. One with everything and one with things defined in RFC 9535 only.

Anything other than those two preconfigured environments, I expect users to do something like this.

from jsonpath import JSONPathEnvironment
from jsonpath.function_extensions import StartsWith


class MyJSONPathEnvironment(JSONPathEnvironment):
    def __init__(self) -> None:
        super().__init__(strict=True)

    def setup_function_extensions(self) -> None:
        super().setup_function_extensions()
        self.function_extensions["startswith"] = StartsWith()


jsonpath = MyJSONPathEnvironment()
query = jsonpath.compile("...")

Do you think this is a reasonable approach? I'll defiantly update the docs and to make this clearer.

[He-Pin]

I think maybe just make sure the predefined one can not be overrided