Adds InputInterpreterTests with:
- Arithmetic cases including precedence, hex/binary, exponent.
- Comparisons yielding numeric booleans.
- Variable assignment (::) and persistence across calls; unknown variable soft error.
- Expression binding (:=) re-evaluated at use-time; invalid expression soft error.
- Array assignment (->) and indexing; out-of-range and index-expression scenarios.
- String literal used as expression soft error.
- Divide-by-zero soft error (no thrown exception).
- LastExecutionTime measured across calls.
Each test asserts both the return value and NumericValue/StringValue for consistency.
