fix(<ARGV>): treat as diamond operator iterating @ARGV

[fglock]

Summary

Fixes ./jcpan -t Slurp which was failing 2/6 subtests due to <ARGV> not behaving like the diamond operator.

In Perl, <ARGV> is identical to the null filehandle <>: it iterates over files named in @ARGV. Previously the parser treated <ARGV> like <STDIN> or <FILE>, emitting a plain readline against the (closed) ARGV filehandle. That broke code like Slurp's:

sub slurp {
    local( $/, @ARGV ) = ( wantarray ? $/ : undef, @_ );
    return <ARGV>;
}

which would emit readline() on unopened filehandle and return nothing.

Special-case <ARGV> in parseDiamondOperator so it produces the same OperatorNode("<>", ...) that <> does, routing through DiamondIO which already handles @ARGV iteration, STDIN fallback, and aliased *ARGV globs.

Test plan

• ./jcpan -t Slurp now PASSes 6/6 (was 4/6)
• make (full unit test suite) passes
• Repro one-liner: local @ARGV = ('/tmp/file1.txt'); my @lines = <ARGV>; now reads the file

Generated with Devin