Refactor option validation and command execution helpers

[mnishiguchi]

Summary

This PR centralizes shared runtime helper logic without changing the public API.

It introduces small internal boundaries for option handling and command execution so synthesis and playback code can stay focused on their own responsibilities.

Changes

• Add OpenJTalk.Options
  • centralizes option validation
  • normalizes playback mode handling
  • normalizes timeout handling
  • provides shared numeric clamping
• Add OpenJTalk.Command
  • wraps command execution behind a small internal boundary
  • keeps MuonTrap usage isolated
  • makes command execution easier to test
• Update synthesis and playback code to use the shared helpers
• Keep OpenJTalk.validate_options!/1 as a compatibility wrapper

Verification

• Confirmed manually in iex -S mix
• Existing public usage remains unchanged