fix(json): do not HTML-escape <, > and & in JSON output

[Sanjays2402]

Closes #552

json.Marshal escapes <, > and & as \u003c, \u003e and \u0026 so the result is safe to embed directly in HTML. dasel writes to files and stdout, so that escaping only makes the output harder to read — dasel -i toml -o json turned "setuptools>=77.0.3" into "setuptools\u003e=77.0.3".

The writer's encoder now uses json.NewEncoder with SetEscapeHTML(false) (trimming the newline Encode appends). TestJsonDoesNotEscapeHTMLCharacters round-trips a string containing <, > and &; it fails on the previous behaviour and passes with the fix. go test ./... is green, and a CHANGELOG entry is included.

This change was prepared with AI assistance; the regression test was run locally and fails without the fix.

[TomWright]

Thank you for the contribution!

Could we add a flag here to allow users to toggle this functionality?

I'm happy with it skipping HTML encoding by default, but it would be good to keep it available for those that need it.

An example of a format specific flat is here:

dasel/parsing/csv/csv.go

Lines 20 to 28 in 70fd28f

	func newCSVWriter(options parsing.WriterOptions) (parsing.Writer, error) {
	w := &csvWriter{
	separator: ',',
	}
	if v, ok := options.Ext["csv-delimiter"]; ok && v != "" {
	w.separator = rune(v[0])
	}
	return w, nil
	}

Something along the lines of json-escape with a value of html should keep escaping