core: #inst instant values + syntax-quote literal collapse (spec 2.3/2.4)

#inst (jolt-rnh): an instant is an immutable tagged struct
{:jolt/type :jolt/inst :ms <epoch-millis>} — equality and map-key hashing by
INSTANT, so different offsets denoting the same moment are =. The reader
parses RFC3339 with Clojure's partial-timestamp defaults (#inst "2020" is
2020-01-01T00:00:00.000Z) and errors on malformed input; inst?/inst-ms in
the overlay; pr-str prints the canonical
#inst "yyyy-MM-ddThh:mm:ss.fff-00:00" and round-trips; str gives the bare
RFC3339 string. Self-evaluating in the evaluator (like uuid/chars).

Syntax-quote (jolt-l2a): a syntax-quoted self-evaluating literal (string,
number, boolean, nil, keyword, char) collapses to the literal at READ time,
matching Clojure's reader — so nested/adjacent backticks over literals are
inert: (= "meow" ```"meow") is true (jank pass-adjacent). Symbols still
qualify and collections still template. General nested syntax-quote over
non-literals remains UNVERIFIED in spec S25.

Tests: inst-spec (18 cases incl. partial defaults, offsets, round-trip),
+10 literal-collapse reader rows, +5 conformance rows (321x3). Spec
02-reader S20/S25 updated to normative. Suite stable 4470/86.

jolt-core/clojure/core/20-coll.clj

@@ -287,6 +287,12 @@
 (defn tagged-literal? [x]     (= (get x :jolt/type) :jolt/tagged-literal))
 (defn record? [x]             (some? (get x :jolt/deftype)))
 (defn uuid? [x]               (= (get x :jolt/type) :jolt/uuid))
+(defn inst? [x]               (= (get x :jolt/type) :jolt/inst))
+
+;; inst-ms: epoch milliseconds of an instant; throws on a non-inst (Clojure
+;; protocol behavior).
+(defn inst-ms [x]
+  (if (inst? x) (get x :ms) (throw (str "inst-ms requires an inst, got: " x))))
 
 ;; Clojure 1.11 map transformers. PHM base so transformed keys canonicalize
 ;; (collisions: last entry in seq order wins, matching the reference).