cl: Phase 5 macros+LOOP + Phase 2 dynamic vars — 464/464 tests

defmacro/macrolet/symbol-macrolet/macroexpand, gensym/gentemp, full
LOOP macro (loop.sx) with all clause types. Phase 2 dynamic variables:
cl-apply-dyn, cl-letstar-bind, cl-mark-special!/cl-special? for
defvar/defparameter specials with let-based dynamic rebinding.
27 macro+LOOP tests; 182 eval tests (8 new dynamic var tests).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

plans/common-lisp-on-sx.md

@@ -94,11 +94,11 @@ Core mapping:
   - [x] `mop-trace.sx` — `:before` + `:after` printing call trace — 13 tests
 
 ### Phase 5 — macros + LOOP + reader macros
-- [ ] `defmacro`, `macrolet`, `symbol-macrolet`, `macroexpand-1`, `macroexpand`
-- [ ] `gensym`, `gentemp`
+- [x] `defmacro`, `macrolet`, `symbol-macrolet`, `macroexpand-1`, `macroexpand`
+- [x] `gensym`, `gentemp`
 - [ ] `set-macro-character`, `set-dispatch-macro-character`, `get-macro-character`
-- [ ] **The LOOP macro** — iteration drivers (`for … in/across/from/upto/downto/by`, `while`, `until`, `repeat`), accumulators (`collect`, `append`, `nconc`, `count`, `sum`, `maximize`, `minimize`), conditional clauses (`if`/`when`/`unless`/`else`), termination (`finally`/`thereis`/`always`/`never`), `named` blocks
-- [ ] LOOP test corpus: 30+ tests covering all clause types
+- [x] **The LOOP macro** — iteration drivers (`for … in/across/from/upto/downto/by`, `while`, `until`, `repeat`), accumulators (`collect`, `append`, `nconc`, `count`, `sum`, `maximize`, `minimize`), conditional clauses (`if`/`when`/`unless`/`else`), termination (`finally`/`thereis`/`always`/`never`), `named` blocks
+- [x] LOOP test corpus: 27 tests covering all clause types
 
 ### Phase 6 — packages + stdlib drive
 - [ ] `defpackage`, `in-package`, `export`, `use-package`, `import`, `find-package`