Adds caching proxy example using HOMEBREW_ARTIFACT_DOMAIN #32297

Job	Run time
syntax	47s
tap syntax	7m 53s
cask audit	2m 52s
formula audit	5m 51s
test default formula (Ubuntu 22.04)	1m 57s
tests (online)	5m 17s
test default formula (Ubuntu 20.04)	2m 48s
update-test (Ubuntu)	23s
tests (generic OS)	3m 29s
test default formula (macOS 13 x86_64)	3m 15s
vendored gems	45s
update-test (macOS)	23s
tests (Ubuntu 24.04)	3m 23s
test default formula (macOS 15 arm64)	1m 16s
tests (Ubuntu 22.04)	3m 23s
tests (Ubuntu 20.04)	3m 33s
tests (macOS 13 x86_64)	7m 46s
tests (macOS 15 arm64)	5m 33s
	1h 0m 34s

Provide feedback