address: Only derive `Copy` if a crate feature is enabled

[joncinque]

Problem

The Address type derives Copy by default, which is very useful in a lot of cases. For example, bytemuck's Pod trait requires all types within to implement Copy.

However, the Copy trait makes it easy to create many more copies than expected, making on-chain programs less efficient.

Proposed Solution

Only derive the Copy trait if a feature is enabled on solana-address.

cc @febo