lib: add the toHex and toBase utility functions

`toHex` converts the given positive integer to a string of the hexadecimal
representation of that integer. For example:

```
toHex 0 => "0"

toHex 16 => "10"

toHex 250 => "FA"
```

`toBase base i` converts the positive integer `i` to a list of it
digits in the given `base`. For example:

```
toBase 10 123 => [ 1 2 3 ]

toBase 2 6 => [ 1 1 0 ]

toBase 16 250 => [ 15 10 ]
```

lib/default.nix

@@ -67,7 +67,7 @@ let
     inherit (trivial) id const pipe concat or and bitAnd bitOr bitXor
       bitNot boolToString mergeAttrs flip mapNullable inNixShell min max
       importJSON warn info showWarnings nixpkgsVersion version mod compare
-      splitByAndCompare functionArgs setFunctionArgs isFunction;
+      splitByAndCompare functionArgs setFunctionArgs isFunction toHex toBase;
     inherit (fixedPoints) fix fix' converge extends composeExtensions
       makeExtensible makeExtensibleWithCustomName;
     inherit (attrsets) attrByPath hasAttrByPath setAttrByPath