Fix stash deletion not removing CODE refs properly

[fglock]

Summary

This fixes a bug where delete ${"Foo::"}{bar} would not properly remove the stash entry when using the ${BLOCK}{key} syntax.

Root Causes Fixed

1. JVM Backend (Dereference.java): The handleHashElementOperator method for ${BLOCK}{key} patterns always called hashDerefGet/hashDerefGetNonStrict regardless of whether the operation was "get", "delete", or "exists".

2. Interpreter (CompileExistsDelete.java): The resolveHashFromBinaryOp method didn't compile operands in SCALAR context, causing -1 register errors when the operand was a BlockNode.

Test Case

package Foo;
sub bar { 42 }

no strict "refs";
print "Before: ", (exists ${"Foo::"}{bar} ? "yes" : "no"), "\n";  # yes
delete ${"Foo::"}{bar};
print "After: ", (exists ${"Foo::"}{bar} ? "yes" : "no"), "\n";   # no (was incorrectly "yes")

Note: Stash deletion removes the stash entry but compiled subroutine references continue to work (matching Perl's CV caching behavior).

Test plan

• Both JVM and interpreter backends correctly return "no" after stash deletion
• op/symbolcache.t passes with same results as master (5/8)
• Build passes

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