Cache Dialyzer PLTs by runtime version

[dashan12344423]

Fixes #18

This updates CI Dialyzer PLT caching so cache keys include the OTP/Elixir runtime and Mix project inputs, reducing stale or incompatible PLT reuse.

Changes:

• Include OTP/Elixir version, mix.exs, mix.lock, and .tool-versions in Dialyzer cache keys
• Apply the same cache key strategy across Lux and Lux App workflows
• Remove a duplicate Dialyzer cache step in lux-app-ci.yml so restore/build/save behavior is consistent

Validation:

• Workflow-only change; reviewed updated cache keys across .github/workflows