fix: add missing setvariabletype in array reduce and numeric find

[cs01]

Summary

• Array reduce() (both numeric and string variants) and numeric find() were missing setVariableType calls on their return values
• This caused downstream type tracking to lose track of what type the result is, which can lead to wrong codegen when the result is used in further operations

Changes

• iteration.ts: Added setVariableType for generateNumericArrayReduce (double) and generateStringArrayReduce (i8*)
• search-predicate.ts: Added setVariableType for generateNumericArrayFind (double)

Test plan

• All 451 compiler tests pass
• Self-hosting Stage 0 + Stage 1 pass