fix(deps): update @actions/cache, @actions/core, @actions/exec, and zod to latest majors

- @actions/cache ^4.1.0 → ^6.0.0
- @actions/core ^1.11.1 → ^3.0.0
- @actions/exec ^1.1.1 → ^3.0.0
- zod ^3.25.76 → ^4.0.0
- Fix zod v4 breaking change: ZodError.errors → ZodError.issues

Closes #35
Closes #36
Closes #37
Closes #38

Author: fengmk2