feat: add json patch support

[ma-ts]

Add json.patch builtin support

Fixes: #95

Implements the json.patch builtin function according to the OPA specification, enabling RFC6902 JSON Patch operations on objects.

Changes

• Added dependency: json-patch crate v4.0.0 with optional jsonpatch feature
• New builtin: json.patch(object, patches) function that applies JSON Patch operations atomically
• Comprehensive tests: Added test cases covering all patch operations (add, remove, replace, move, copy, test)

Features

• Supports all RFC6902 patch operations
• Atomic application - if any patch fails, result is undefined
• Works with nested objects, arrays, and special characters in keys
• Proper error handling in both strict and non-strict modes

Usage

# Add a new field
json.patch({"a": {"foo": 1}}, [{"op": "add", "path": "/a/bar", "value": 2}])
# Result: {"a": {"foo": 1, "bar": 2}}

# Multiple operations
json.patch(obj, [
  {"op": "add", "path": "/a/bar", "value": 2},
  {"op": "replace", "path": "/a/foo", "value": 42}
])

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[anakrish]

@ma-ts Thanks for the contribution. Do also add v0/jsonpatch and v1/jsonpatch to https://github.com/microsoft/regorus/blob/main/tests/opa.passing to ensure that the OPA jsonpatch tests get run.

I happened to see that you have also created feature request in the Azure Policy repo. We are working on some interesting projects involving Azure Policy and Regorus. Hence, I'm curious whether you are already using Regorus.

[ma-ts]

Hi @anakrish, I will do that! And yes, all of this is part of a big policy overhaul in our organisation, and actually we are already using it in some services.

I am soon going to be open sourcing a project as well to provide a Rust-based ingress controller that uses Regorus and integrates natively with OIDC, and has special support for Entra ID

[anakrish]

https://docs.rs/serde_json/latest/serde_json/fn.from_value.html and https://docs.rs/serde_json/latest/serde_json/fn.to_value.html can be used to avoid explicit serialization to strings.

[anakrish]

Suggested change

	let mut object: serde_json::Value = serde_json::from_str(&object_str)
	let mut object: serde_json::Value = serde_json::to_value(&args[0])

[anakrish]

Suggested change

	let patches_json: serde_json::Value = serde_json::from_str(&patches_str)
	let patches_json: serde_json::Value = serde_json::to_value(&args[1])

[anakrish]

Suggested change

	let result_str = serde_json::to_string(&object)
	let value : regorus::Value = serde_json::from_value&object)

[anakrish]

Hey @ma-ts, just a gentle ping on this.