Avoid parameter mutation during deref; add test for parameter mutation across runs

[daniellmorrisGP]

Summary

• Replace cloneDeep usage with a shallow copy + deref in the closure
  handler to prevent mutating original parameters.
• Make deref of arrays/objects operate on copied inputs.
• Add a test ensuring closure parameter mutation does not persist
  across runs.

Details

• src/index.ts: switch to { ...(contextExt?.parameters ?? {}) }
  before deref; copy arrays/objects in dereferenceSingleValue.
• tests/unit/rules_worker.test.ts: new test Closure parameter
  mutation does not persist across runs.