Add universal receiver handlers to contracts

[ya7on]

Is your feature request related to a problem

During some cases (e.g. sending Excess to Lock contract) some transactions fail with exit code 130, indicating that the contract does not implement a catch-all message receiver (receiver (msg: Slice) { }).

Describe the solution you'd like

Implement a default receiver (msg: Slice) { } handler (aka "universal receiver") in the following contracts:

• Lock
• Skipper
• Proposal
• Voter

This handler should:

1. Accept any incoming message (generic fallback).
2. Optionally use the received TON to top up the contract’s gas reserve.
3. Return change (leftover funds) to the sender, minus a fixed reserved amount (e.g., 0.05 TON for gas).

This would act as a safe "top-up" API and eliminate issues from unknown incoming messages.

Describe alternatives you've considered

No response

Additional context

No response