fix(peer-store): copy observation times from the matching address

[tabcat]

Description

Each stored address is stamped with an observed timestamp, copied from the
matching existing address so a re-stored address keeps its original time. The
lookup for the matching address named its callback parameter addr, shadowing
the address being stamped, so it compared an address to itself and always
matched the first stored address. Every address therefore inherited the first
stored address's observed time instead of its own, so a newly added multiaddr
could be expired early by maxAddressAge despite having just been observed.

Rename the callback parameter so the lookup matches by multiaddr.

Change checklist

• I have performed a self-review of my own code
• I have made corresponding changes to the documentation if necessary (this includes comments as well)
• I have added tests that prove my fix is effective or that my feature works