Support merging types with multiple regex validations (allOf).

[inickles]

I tried running Typify on a schema that had an allOf declaration:

    "EmailAddressDatatype": {
      "description": "An email address string formatted according to RFC 6531.",
      "allOf": [
        {
          "$ref": "#/definitions/StringDatatype"
        },
        {
          "type": "string",
          "format": "email",
          "pattern": "^.+@.+$"
        }
      ]
    },

but this resulted in an error: Message: not implemented: merging distinct patterns is impractical

This PR handles the case of multiple regex validation patterns by chaining them with lookaheads.

Consider the test code in this PR at typify-impl/tests/all_of.json:

{
    "$schema": "http://json-schema.org/draft-07/schema#",
    "definitions": {
        "TriplePattern": {
            "allOf": [
                {
                    "type": "string",
                    "pattern": "^[a-z].+$",
                    "format": "custom-id"
                },
                { "type": "string", "pattern": "^.{4,8}$" },
                { "type": "string", "pattern": ".+[a-z]$" }
            ]
        }
    }
}

Regex validation for this will now result in:

::regress::Regex::new("(?=^[a-z].+$)(?=^.{4,8}$)(?=.+[a-z]$)")

This adds a new test all_of in typify-test/src/main.rs that verifies this functionality works as expected. It uses that all_of.json, which is also used for an integration test in testify-impl.

Fun fact, the original schema I was trying to process was the NIST OSCAL schema at https://github.com/usnistgov/OSCAL/releases/download/v1.2.2/oscal_catalog_schema.json. I am able to successfully run Typify on that schema with this PR. The pattern for that EmailAddressDatatype type results in:

::regress::Regex::new("(?=^\\S(.*\\S)?$)(?=^.+@.+$)")