Phase 6: slurp, spit, read-line, range 3-arg, repeat/cycle/iterate, interleave

Phase 6 Clojure Core Library now complete (except meta):
- T6.3: slurp (alias for file/read)
- T6.4: spit (alias for file/write)
- T6.5: read-line (stdin input)
- T6.6: range with 3 args (start, end, step)
- T6.7: repeat, cycle, iterate (eager implementations)
- T6.9: interleave
- Updated TASKS.md and ROADMAP.md

docs/ROADMAP.md

@@ -53,10 +53,10 @@
 - [ ] Transients for batch mutations
 
 ## Phase 6: Clojure Core Library
-- [ ] `range`, `repeat`, `cycle`, `iterate`
+- [x] `range` (0/1/2/3 args), `repeat`, `cycle`, `iterate`
 - [x] `take`, `drop`, `partition`, `interleave`, `concat`
 - [x] `str`, `pr-str`, `println`, `prn`
-- [ ] `slurp`, `spit`, `read-line`
+- [x] `slurp`, `spit`, `read-line`
 - [ ] `meta`, `with-meta`, `vary-meta`
 - [x] `type`, `instance?`, `satisfies?`