* refactor: add more details to error logs in ip cache
* refactor: improve logs for ip cache set methods
* code review: warn if cannot obtain any source address
* refactor: error if cannot obtain any source address
* code review: better variable naming
* refactor: avoid repeated subscripting in `announcer-udp.cc`
* chore: remove redundant locking in global ip cache
* chore: misc code cleanup in global ip cache
* fixup! chore: misc code cleanup in global ip cache
* refactor: remove `tr_global_ip_cache::create()`
* refactor: rename `tr_global_ip_cache` to `tr_ip_cache`
* build: sync changes to xcode
