Use legacy Zaino NU6.2 backport

[czarcas7ic]

This keeps Zallet on the legacy Zaino 0.1 line and repins the Zaino crates to the Valar NU6.2 backport commit.

The intent is to avoid the broad Zaino 0.2/ChainIndex bump that forces operators to build a persistent Zaino cache database, while still allowing Zallet to start against Zebra nodes that report NU6.2 at the tip.

Validation:

• cargo check -p zallet --locked
• disposable startup against synced Zebra v5.0.0-rc.3 reached chain tip and did not create a zaino cache directory

Draft caveats:

• legacy Zaino still logs invalid consensus branch id while parsing some NU6.2 mempool transaction data. Startup and tip sync continue, but that warning should be evaluated before promoting this as final.
• the latest-deps CI jobs delete Cargo.lock and fail on the inherited zebra-chain 2.0 / yanked orchard 0.11 resolver path. The locked build check passes.
• the NU7 CI job fails in the inherited zebra-chain 2.0 code path because zcash_unstable="nu7" exposes a Nu7 enum variant that zebra-chain 2.0 does not match. This branch does not change zebra-chain or zcash_protocol.