feat: Add JSON configuration parser

[FumingPower3925]

Adds a new parser to support loading configuration values from JSON files.

Includes:

• json package with the parser implementation.
• Comprehensive unit tests covering various JSON structures and edge cases.
• Fix for handling null values in the core ToString conversion function.

[chaindead]

also, why you need raw json parser?

i understand if it is remote source or smth like this that provides json configuration, but i do not see cases of using file in json over yaml

[FumingPower3925]

also, why you need raw json parser?

i understand if it is remote source or smth like this that provides json configuration, but i do not see cases of using file in json over yaml

Well, in my workplace we use JSON for configs as a standard, so I am kind of used to it. I do not have anything against YAML, however, I find JSON configs to handle better really complex application configs, I find them easier to maintain.

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[FumingPower3925]

I've added the changes you requested on treating as errors missing file, empty file and malformed file.

I've not changed from decode to unmarshall as I still believe that maintaining the expressiveness of the number values in json is important. However, as I said in another comment, if you tell me so, I will change it to use Unmarshall.

[chaindead]

i thought how json support should be implemented, here what i think

example code to fetch from url with file support

package main

import (
	"fmt"
	"io"
	"net/http"
	"net/url"
	"os"
	"strings"
)

func fetchJSON(u *url.URL) ([]byte, error) {
	var reader io.ReadCloser
	var err error

	switch u.Scheme {
	case "http", "https":
		resp, err := http.Get(u.String())
		if err != nil {
			return nil, fmt.Errorf("http get failed: %w", err)
		}
		if resp.StatusCode != http.StatusOK {
			resp.Body.Close()
			return nil, fmt.Errorf("http status: %s", resp.Status)
		}
		reader = resp.Body
	case "file":
		// Normalize the file path
		path := u.Path
		if u.Host != "" {
			// Handle Windows UNC-style paths like file://host/path
			path = "//" + u.Host + u.Path
		}
		reader, err = os.Open(path)
		if err != nil {
			return nil, fmt.Errorf("file open failed: %w", err)
		}
	default:
		return nil, fmt.Errorf("unsupported URL scheme: %s", u.Scheme)
	}
	defer reader.Close()

	data, err := io.ReadAll(reader)
	if err != nil {
		return nil, fmt.Errorf("read failed: %w", err)
	}
	return data, nil
}

• add URL configuration option support like

url:=zfg.URL("name", "file:///a/b/c.json", "path to json config")
and json provider api like this
json.New(url)

• add json provider description to readme section

but there another option:

• add community providers section to readme
• add your provider with link to your repo

[FumingPower3925]

I've added the URL support as you described. I find it a great idea!

[chaindead]

add test to z_test.go for url, use struct like

type urlVale url.Url

[FumingPower3925]

I've modified z_url to use type urlVale url.Url.
Added the tests in z_test.go for url.