Add test cases demonstrating that the reduce function works with string arrays
and concatenation, verifying both with and without initial accumulator values.
The test uses a list of characters ["W", "o", "r", "l", "d"] and the existing
sum function to show that reduce correctly folds strings in order.
Add a new test file `test/range/reduce.wren` that validates the `reduce` method on numeric ranges. The test exercises two cases: summing integers 1 through 10 (expecting 55) and finding the minimum value with an initial accumulator of 100 (expecting 1).
Replace the previous slice-based single-argument reduce implementation with an explicit iterator loop that seeds from the first element. This avoids the out-of-bounds range error on single-element lists and adds a Fiber.abort for empty sequences. Update the test to verify correct behavior for single-element and empty sequences.
Implement `reduce` on the `Sequence` class in core.wren with two overloads: one taking an initial accumulator and a function, and another using the first element as the initial accumulator. Add three test files covering normal reduction, single-element edge case, and wrong arity error.
Luchs