Support control flow for all labeled blocks

[fglock]

Extends the control flow fix from PR #121 to work with all labeled blocks, not just SKIP.

Changes

• EmitBlock.java: Registry check now applies to all labeled blocks (not restricted to SKIP only)
• skip_control_flow.t: Added 6 new test cases for TODO and CLEANUP labels

Why This Change

PR #121 implemented control flow support for SKIP blocks, but the mechanism should work for any labeled block (TODO, CLEANUP, or any custom label). There's nothing special about the SKIP label name.

Test Results

All 9 tests pass:

• ✅ Tests 1-3: SKIP labeled blocks (single frame, scalar context, void context)
• ✅ Tests 4-6: TODO labeled blocks (single frame, scalar context, void context)
• ✅ Tests 7-9: CLEANUP labeled blocks (single frame, scalar context, void context)

Example

sub inner { last TODO }
sub outer { my $x = inner(); return $x; }
TODO: {
    print "A";
    my $r = outer();  # Control flow propagates through function call
    print "B";       # This is skipped
}
print "C";           # Execution continues here
# Output: AC

This works for any label name: SKIP, TODO, CLEANUP, or custom labels.