Check address and key lengths when parsing strings

[teor2345]

Scheduling

We don't need to fix these bugs until we start full wallet work.

Motivation

Zebra doesn't check the length of address or key strings when parsing.

This might lead to loss of funds.

Specifications

The Zcash consensus rules say that keys and addresses should be a specific length.

Designs

In methods that handle untrusted data:

• From
• FromStr

Check that the key or address is the correct length, and return an error if there is any trailing data.

This issue applies to all keys and addresses in Zebra.