[Perl/perl5] d62dd4: `GetOpt::Std`: Fix import methods

[Elvin Aslanov via perl5-changes]

  Branch: refs/heads/blead
  Home:   https://github.com/Perl/perl5
  Commit: d62dd48c3ee7e6e5cee9d356fc1874492bbd930b
      
https://github.com/Perl/perl5/commit/d62dd48c3ee7e6e5cee9d356fc1874492bbd930b
  Author: Elvin Aslanov <rwp.prim...@gmail.com>
  Date:   2023-09-18 (Mon, 18 Sep 2023)

  Changed paths:
    M lib/Getopt/Std.pm
    M lib/Getopt/Std.t

  Log Message:
  -----------
  `GetOpt::Std`: Fix import methods

Also some minor documention, formatting, styling

Fixes https://github.com/Perl/perl5/issues/21465

Add `\my %opt` syntax tests per @jkeenan