fix(builders): count signers only for required native scripts

[penielgold-hub]

Summary

Fix fee estimation so fake signer witnesses are added only for native scripts the transaction actually requires.

Previously, buildFakeWitnessSet counted required signers for every native script carried by reference inputs or spent inputs, even when the transaction did not use those scripts. That could overestimate the transaction size and fee.

This change:

• collects script hashes required by spending, minting, certificates, withdrawals, voting, and proposals
• counts native-script signers only for those required hashes
• deduplicates required script hashes
• preserves attached native scripts in the fake witness set for transaction-size estimation
• keeps existing native-script signer counting for genuinely required scripts

Tests

• added regression coverage for unrelated native scripts carried by spent inputs
• added regression coverage for unrelated native scripts carried by reference inputs
• added certificate signer-estimation coverage
• tightened the proposal guardrail signer assertion

Verified locally:

• new signer-estimation tests: 3 passed
• ProposeGuardrail tests: 18 passed
• related native-script builder tests: 22 passed
• type-check: passed
• lint: passed
• git diff --check: passed

Closes #596