transduce-reduce and core-reduce both called realize-for-iteration, fully
realizing the coll before the reduce loop — so an infinite lazy seq hung before
the reduced short-circuit could fire. (into [] (take 5) (range)) etc. never
terminated.
Add reduce-with-reduced, which steps a lazy seq one cell at a time
(realize-ls/ls cell protocol), checking reduced? after each element so a take/
take-while transducer (or any reducing fn returning reduced) terminates over an
infinite seq. Route transduce-reduce and both core-reduce arities through it;
2-arg reduce now seeds from the first element and reduces the rest lazily.
spec: transducers/short-circuit + reduce/honors-reduced (13 cases).
clojure-test-suite timeouts 7->6, pass 1683->1688. jpm test green.
Fixes jolt-kxb.
2885650ef6