Preflight aggregate mixed-input signing size

[rohenaz]

Summary

• project every planned unlocking script at the pinned SDK safe maximum before any input-key derivation or wallet signature request
• use TransactionInput pay-to-public-key-hash and PushDrop maximum unlocking-script constants rather than storage estimates
• validate the completed projected transaction with serializedByteCount and caller limits
• resolve all ordinary BRC-29 input keys before invoking any permission-token signer

Regression

A two-token action constrained to the maximum size of only one projected token now fails before either signer runs.

Tests

• swift test --filter BRC116ActionSignerTests — 12 passed
• swift test — 221 executed, 10 expected live-environment skips, 0 failures

Follow-up to PR #10. This PR is intentionally limited to ActionSigner and its focused tests.