Optimize away unused optional globals (__tact_child_contract_codes, __tact_randomized) #3326

Currently, optional global variables __tact_child_contract_codes and __tact_randomized are always included in the generated FunC output, even when they're never used by the contract. These globals can be safely omitted when unused, leading to a minor gas-saving improvement per execution.

Task:

• Detect whether __tact_child_contract_codes and __tact_randomized globals are actually used.
• Omit these globals entirely from FunC output when not referenced.

Impact:
This optimization results in a slight improvement in gas usage (saving a few gas points per execution) and reduces contract byte size minimally.