ci: add Docker layer caching to context guard and timeouts to all jobs #497

Job	Run time
Build (ubuntu-latest)	4m 56s
Format Check	13s
Build (macos-latest)	10m 27s
Docker Context Guard	7m 52s
Marketplace Packer Validate	7s
Cargo Package Verify	3m 41s
Compose File Validate	5s
Bun Ecosystem Checks	6s
CLI Parity Tests	19s
E2E Tests	3m 48s
	31m 34s

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