`test_mnemonic_vectors_from_file` takes a long time to run against current live chain state

[EchoAlice]

Summary

test_mnemonic_vectors_from_file appears to be live-chain-dependent and currently takes a very long time to complete against the current environment.

Observed Behavior

cargo test test_mnemonic_vectors_from_file -- --nocapture

• the test starts and creates a new wallet from vector 0
• it spends long stretches in PollReport::NotReady
• progress may be extremely slow / uneven
• on instrumented runs, some birthdays eventually showed partial scan progress, but the test still did not provide a fast or clean end-to-end validation signal

Notes

This reproduces on main, so it does not appear to be introduced by PR #61.

My current guess is that this test is too live-chain / runtime / pinned-dependency dependent to be a reliable validation path in its current form.

Possible follow-ups

• mark this test ignored / explicitly live-chain-dependent
• replace this with a more controlled test that does not depend on current chain state
• update the pinned zingolib revision
• investigate whether the current fixture / birthday strategy is making the test especially noisy

Opening this mainly to separate the pre-existing mnemonic test/runtime issue from PR #61.