Improve generated syntax

[agu-z]

I tried to generate elm icon modules out of the entire FontAwesome 6 distribution and found a couple of syntactic errors in the generated output. This PR addresses all of them:

• When generating a function for a file name that starts with a number, prefix the name with n to generate a valid Elm identifier.
• Handle comments between SVG nodes.
• elm-format compliant (addresses Generated code is not valid according to elm-format #9):
  • No redundant parenthesis
  • Function expression in an indented new line
  • Surround non-empty list elements with spaces
  • Surround comments with spaces and trim content
  • Two empty lines between declarations
  • End file with a newline