Add Phase 3 debugger features: p/x commands, %DB::sub, @DB::args

[fglock]

Summary

This PR adds Phase 3 features to the Perl debugger:

• p expr command: Evaluate and print expressions in the debugger
• x expr command: Dump expressions with Data::Dumper formatting
• %DB::sub hash: Track subroutine locations (file:startline-endline)
• @DB::args array: Capture subroutine arguments on each call

Bug Fixes

• Step-into subroutines: Fixed by tracking callDepth with enterSubroutine()/exitSubroutine() calls
• DEBUG opcode line numbers: Fixed incorrect line numbers for lazily compiled subroutines by using getLineNumberAccurate() which counts from the beginning of the file
• Disassembler: Added DEBUG opcode support for better debugging

Testing

$ ./jperl -d script.pl
main::(script.pl:5):
5:  foo(10, 20);
  DB<1> s
main::(script.pl:2):
2:  my ($x, $y) = @_;
  DB<2> p "@DB::args"
10 20
  DB<2> x \@DB::args
$VAR1 = [
          10,
          20
        ];

Test plan

• All existing tests pass
• Step into subroutines works correctly
• Breakpoints inside subroutines work
• @DB::args shows correct arguments
• %DB::sub tracks subroutine locations

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