refactor: rename dynamic-vars.ss, extract natives-format.ss (jolt-7dkx)

Two small clarity moves from the review:
- dynamic-vars.ss -> dynamic-var-defaults.ss. It holds the default VALUES of a few
  core dynamic vars (*clojure-version*, *assert*, …); the near-identical dyn-binding.ss
  holds the binding-stack machinery. The names were easy to confuse.
- Pull the ~60-line %-format engine out of the natives-misc.ss grab-bag into
  natives-format.ss (its ->long/pad-left/fmt-float helpers were local to it).
rt.ss loads + MODULES.md updated. Runtime .ss, no re-mint; make test green, format +
the dynamic vars verified.

host/chez/dynamic-vars.ss

@@ -1,25 +0,0 @@
-;; dynamic vars — the handful of clojure.core dynamic vars that aren't emitted into
-;; the prelude. These two are plain constants; *ns* (a namespace object) needs a
-;; value type with get-see-through and map?=false and is tracked separately. Loaded
-;; from rt.ss after the value model + def-var!.
-
-;; *clojure-version* — a map {:major 1 :minor 11 :incremental 0 :qualifier nil}.
-(def-var! "clojure.core" "*clojure-version*"
-  (jolt-hash-map (keyword #f "major") 1
-                 (keyword #f "minor") 11
-                 (keyword #f "incremental") 0
-                 (keyword #f "qualifier") jolt-nil))
-
-;; *unchecked-math* — jolt does no unchecked-math elision; the var reads false.
-(def-var! "clojure.core" "*unchecked-math*" #f)
-
-;; *warn-on-reflection* — jolt has no reflection, so the var reads false; (set!
-;; *warn-on-reflection* …) resolves and updates it (a no-op effect).
-(def-var! "clojure.core" "*warn-on-reflection*" #f)
-
-;; *assert* — gates `assert`; settable/bindable (malli.assert toggles it). Default
-;; true, like the JVM.
-(def-var! "clojure.core" "*assert*" #t)
-
-;; *print-readably* — bound by pr-family / with-out-str-style code; default true.
-(def-var! "clojure.core" "*print-readably*" #t)