feat: add/support stop_grace_period

[jpagh]

Summary

Adds support for Compose’s stop_grace_period service option.

Container Compose now:

• Parses Compose duration values such as 30s, 1m30s, and fractional values
• Uses Compose’s default 10-second timeout when omitted
• Passes the configured timeout to Apple Container when:
  • Running container-compose down
  • Replacing existing containers during up
  • Stopping foreground containers with Ctrl+C
• Preserves the image’s configured stop signal, falling back to SIGTERM
• Rejects invalid or out-of-range durations

Example

  services:
    app:
      image: alpine:latest
      stop_grace_period: 75s

Testing

• Added static tests covering:
  • Combined durations
  • Default timeout behavior
  • Fractional-second truncation
  • Invalid durations
  • Apple Container stop-option conversion
• Added a dynamic test confirming that the configured deadline is enforced
• Manually verified with a real container that traps SIGTERM, waits 70 seconds, and exits:
  • Configured stop_grace_period: 75s
  • container-compose down waited 71 seconds
  • The container completed its graceful shutdown instead of being killed after the default 10 seconds