The `hexenc()` function encodes the given byte string into a hexadecimal
digit string, converting the input value to a string if needed.

Returns the encoded hexadecimal digit string.

-- Testcase --
{%
	printf("%.J\n", [
		hexenc("Hello world!\n"),  	// encoding a simple string
		hexenc(""),  				// empty input -> empty output
		hexenc([1, 2, 3]),  		// implicit stringification
		hexenc(null),  				// null input -> null output
	]);
%}
-- End --

-- Expect stdout --
[
	"48656c6c6f20776f726c64210a",
	"",
	"5b20312c20322c2033205d",
	null
]
-- End --